Digital air gun

ABSTRACT

A marine air gun generates an acoustic signal in water, for example, during a marine seismic survey. The marine air gun includes digital electronic circuitry. The digital electronic circuitry may control an actuator of the marine air gun, digitize and store data from sensors located on or near the marine air gun, send and/or receive digital communications, store and/or output electrical energy, and/or perform other functions. A marine seismic source system that includes multiple air gun clusters may have a separate digital communication link between a command center and each air gun cluster. Each communication link may provide power and digital communication between the command center and one of the air gun clusters.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of co-pending provisionalapplication Ser. No. 61/217,204, filed May 28, 2009 and entitled “MarineSeismic Airgun with Internal Monitoring and Related Control Systems andMethods,” the entire contents of which is incorporated herein byreference. This application incorporates by reference the entirecontents of commonly owned international application numberPCT/2010/036423, entitled “Digital Air Gun,” concurrently filed with theU.S. Receiving Office under the Patent Cooperation Treaty.

BACKGROUND

Air guns are used as a source of seismic energy for marine seismicsurveys. Air guns are typically deployed in an air gun array towed by avessel. The air gun array can include several clusters of air guns, eachsubmersed in water and suspended from a flotation device towed by thevessel. The vessel controls the air gun array to generate seismic sourcesignals. To generate a seismic source signal the vessel fires the airguns in the array simultaneously, and the resulting seismic signalinteracts with geological features beneath the ocean floor. Reflectedseismic signals are collected and analyzed to identify properties ofsubsurface geological formations.

SUMMARY

In one general aspect, a marine air gun includes digital electroniccircuitry. The digital electronic circuitry may control an actuator ofthe marine air gun, digitize and store data from sensors located on ornear the marine air gun, send and/or receive digital communications,store and/or output electrical energy, and/or perform other functions.

In another general aspect, a marine seismic system includes a digitalcommunication system. The digital communication system may include aseparate digital communication link between a command center and eachair gun cluster.

In some aspects, a marine air gun includes a pressure release assembly,an actuator, and a digital electronic controller. The pressure releaseassembly releases compressed air into water to generate an acousticsignal. The actuator moves to actuate the pressure release assembly inresponse to an electrical signal applied to the actuator. The actuatoris carried by the pressure release assembly. The digital electroniccontroller controls the electrical signal applied to the actuator. Thedigital electronic controller is carried by the pressure releaseassembly.

Implementations may include one or more of the following features. Themarine air gun includes one or more sensors carried by the pressurerelease assembly. The one or more sensors include a depth transducer, apressure transducer, and/or a zero-field hydrophone. The digitalelectronic controller includes a digitizer that receives analog datafrom the one or more sensors and converts the analog data to digitaldata. The digital electronic controller includes a memory that storesthe digital data. The marine air gun includes a communication interfacecarried by the pressure release assembly. The communication interface isconfigured to transmit the digitized data from the digital electroniccontroller to a central control system external the marine air gun. Thecommunication interface is configured to receive digital communicationsfrom the central control system. The digital communications includecommands that operate the digital electronic controller. The marine airgun includes a high voltage supply carried by the pressure releaseassembly. The high voltage supply is electrically coupled to theactuator by a switch. The digital electronic controller is communicablycoupled to the switch to control the electrical signal applied to theactuator by the high voltage supply. The high voltage supply includestwo capacitors each receiving an input voltage. The capacitors areconnected in series to provide an output voltage twice the inputvoltage. One or both of the capacitors is an electrolytic capacitor. Themarine air gun includes a circuit board carried by the pressure releaseassembly. The circuit board includes the digital electronic controller,a low voltage supply, a high voltage supply, and a communicationinterface. The actuator and the digital electronic controller reside inan actuator housing carried by a separate housing of the pressurerelease assembly. The actuator and/or the digital electronic controllerreside in a chamber defined by a housing of the pressure releaseassembly. The pressure release assembly defines one or more ports andincludes a pressure chamber that stores the compressed air. The pressurerelease assembly includes a partition that prevents fluid communicationbetween the chamber and the one or more ports. Actuation of the pressurerelease assembly moves the partition to permit communication of thecompressed air into the water from the chamber through the one or moreports. The actuator is a solenoid valve. A component of the solenoidvalve moves to release a pneumatic signal in response to the electricalsignal applied to the actuator. The pneumatic signal moves the partitionto permit communication of the compressed air into the water from thechamber through the one or more ports.

In some aspects, a marine seismic system includes a sensor that detectsconditions in or about a marine air gun submersed in water. The marineair gun includes a pressure release assembly that generates an acousticsignal. The marine air gun includes a digitizer that converts analogdata from the sensor to digital data. The digitizer is carried by thepressure release assembly and communicably coupled to the sensor. Themarine air gun includes a memory that stores the digital data. Thememory is carried by the pressure release assembly and communicablycoupled to the digitizer.

Implementations may include one or more of the following features. Thesensor includes a zero-field hydrophone carried by the pressure releaseassembly. The zero-field hydrophone detects acoustic data in the waterabout the marine air gun. The sensor includes a near-field hydrophonespaced apart from the marine air gun. The near-field hydrophone detectsacoustic data in the water about the marine air gun. The sensor includesa depth transducer carried by the pressure release assembly. The depthtransducer detects a depth of the marine air gun below a surface of thewater. The sensor includes a pressure transducer carried by the pressurerelease assembly. The pressure transducer detects an internal pressurein a chamber in the pressure release assembly. The sensor resides in asensor housing carried by a housing of the pressure release assembly. Adigital electronic controller that includes the digitizer and the memoryreside in a controller housing carried by a housing of the pressurerelease assembly. The marine air gun includes a communication linkbetween the sensor housing and the controller housing. A digitalelectronic controller includes the digitizer and the memory. The sensorand the digital electronic controller reside in a control housingcarried by a housing of the pressure release assembly. The sensor iscommunicably coupled to the digital electronic controller by a solderedconnection in the control housing. The marine air gun includes a digitalelectronic controller that includes the digitizer and the memory. Themarine air gun includes an actuator that moves to actuate the pressurerelease assembly in response to an electrical signal applied to theactuator. The digital electronic controller controls the electricalsignal applied to the actuator. The digital electronic controller andthe actuator reside in a control housing carried by the pressure releaseassembly.

In some aspects, a marine seismic system includes an array of marine airguns and a central control subsystem. Each of the marine air gunsincludes a digital electronic controller and/or one or more featuresdescribed above. The central control subsystem is communicably coupledto the digital electronic controller of each marine air gun to sendpower and communications to the marine air gun.

Implementations may include one or more of the following features. Thesystem includes communication links that communicably couple the centralcontrol subsystem to the marine air guns to transmit the power andcommunications. Each marine air gun includes a communication interfacethat communicably couples one of the communication links to the digitalelectronic controller. The system includes a multiplexer communicablycoupled to the central control subsystem and the plurality ofcommunication links. The multiplexer receives multiplexed signals fromthe central control subsystem, demultiplex the multiplexed signals, andsends the demultiplexed signals to the marine air guns through thecommunication links. The multiplexer may also receive signals from themarine air guns, multiplex the multiplexed signals, and send themultiplexed signals to the central control subsystem. The array includesmultiple air gun clusters. Each of the air gun clusters includes one ortwo of the marine air guns. Each communication link providescommunication and power from the central control subsystem to a singlecluster. Each marine air gun includes a communication interfaceconfigured to transmit digital data from the digital electroniccontroller of the marine air gun to the central control subsystem. Thecommunication interface is carried by the pressure release assembly. Thecentral control subsystem resides on a marine vessel that tows thearray.

In some aspects, a marine seismic system includes multiple air gunclusters and a central control subsystem. Each air gun cluster includesone or more marine air guns that generate acoustic signals in waterbased on digital communications from the central control subsystem. Thecentral control subsystem is communicably coupled to the air gunclusters by multiple communication links. Each of the communicationlinks is communicably coupled to one of the air gun clusters to transmitthe digital communications from the central control subsystem to the airgun cluster.

Implementations may include one or more of the following features. Thecommunication link for each air gun cluster is a single twisted pairand/or multiple twisted pairs. Each marine air gun cluster is configuredfor bidirectional communication with the central control subsystem overthe single twisted pair and/or over multiple twisted pairs. Thecommunication link for each air gun cluster is a fiber optic link. Eachmarine air gun includes a digital electronic controller. The digitalcommunications include commands transmitted from the central controlsubsystem to the digital electronic controller. Each air gun includes asensor. The digital communications include data collected by the sensorand transmitted from the marine air gun to the central controlsubsystem.

In some aspects, communicating digital data in a marine seismic systemincludes sending an outgoing digital communication to a marine air gunby modulating voltage on a communication link that couples the marineair gun to a central control subsystem. An incoming digitalcommunication from the marine air gun is detected based on currentmodulations on the communication link. The incoming digitalcommunication is stored in a memory of the central control subsystem.

Implementations may include one or more of the following features. Theincoming digital communication includes digital data collected bysensors at the marine air gun. The outgoing digital communicationincludes digital command signals that control operation of the marineair gun. The communication link includes a first conductive wire and asecond conductive wire. Modulating voltage on the communication linkincludes switching between a first voltage state and a second voltagestate. In the first voltage state, the first conductive wire iselectrically coupled to a high voltage source and the second conductivewire is electrically coupled to a ground reference voltage. In thesecond voltage state, the second conductive wire is electrically coupledto the high voltage source and the first conductive wire is electricallycoupled to the ground reference voltage. The high voltage sourceincludes a 40 Volt direct current voltage source, and the groundreference voltage is 0 Volts. Detecting an incoming digitalcommunication from the air gun based on current modulations on thecommunication link includes converting changes in current on thecommunication link to binary voltage signals. A change in current isconverted to a binary voltage signal by outputting a first voltage statebased on detecting an increase in the current on the communication linkand/or outputting a second voltage state based on detecting a decreasein the current on the communication link.

In some aspects, communicating digital data in a marine seismic systemincludes sending an outgoing digital communication from a marine air gunby modulating current on a communication link that couples the marineair gun to a central control subsystem. An incoming digitalcommunication is detected from the central control subsystem based onvoltage modulations on the communication link. The incoming digitalcommunication is stored in a memory of the marine air gun.

Implementations may include one or more of the following features. Theoutgoing digital communication includes digital data collected bysensors at the marine air gun and the incoming digital communicationincludes digital command signals that control operation of the marineair gun. Modulating current on the communication link includes togglingan electrical coupling between the communication link and a groundreference voltage. The electrical coupling includes a switch and aresistor connected in series between the communication link and theground reference voltage. Toggling the electrical coupling includeschanging the switch between a conductive state and a non-conductivestate. Detecting an incoming digital communication from the centralcontrol subsystem based on voltage modulations on the communication linkincludes converting voltage differences on the communication link tobinary voltage signal. A voltage difference is converted to a binaryvoltage signal by comparing a first voltage on a first conductor of thecommunication link and a second voltage on a second conductor of thecommunication link, outputting a first voltage state when the firstvoltage is higher than the second voltage, and/or outputting a secondvoltage state when the second voltage is higher than the first voltage.Electrical power is received from the communication link. The electricalpower is used to operate electronic circuitry of the marine air gun.Receiving the electrical power includes receiving the electrical powerconcurrently with detecting the incoming digital communication.

In some aspects, a marine seismic system includes a communication link,a central control subsystem, and a marine air gun. The communicationlink transmits digital data between the central control subsystem andthe marine air gun. The central control subsystem includes a voltagemodulator coupled to the communication link to transmitvoltage-modulated signals to the marine air gun. The marine air gunincludes a current modulator coupled to the communication link totransmit current-modulated signals to the central control subsystem.

Implementations may include one or more of the following features. Thevoltage-modulated signals and the current-modulated signals each includeasynchronous and/or synchronous digital communications. Thecommunication link is a twisted pair. The system includes additional airguns and additional communication links. Each additional air gunincludes a current modulator coupled to one of the additionalcommunication links to transmit current-modulated signals to the centralcontrol subsystem. The central control subsystem includes additionalvoltage modulators each coupled to one of the additional communicationlinks to transmit voltage-modulated signals to one of the air guns. Themarine air gun includes a comparator that converts the voltage-modulatedsignals to binary data, and the marine air gun includes a memory thatstores the binary data. The central control subsystem includes aset-reset device that converts the current-modulated signals to binarydata, and the central control subsystem includes a memory that storesthe binary data. The voltage modulator includes an H-bridge. The currentmodulator includes a transistor.

In some aspects, a marine air gun includes an actuation device, asolenoid, a solenoid housing, and a transducer housing. The transducerhousing may be bolted onto the solenoid housing. The solenoid may behoused and contained within a sealed space formed by and between thesolenoid housing and the transducer housing. The marine air gun mayinclude circuitry for controlling the solenoid. The circuitry mayinclude one or more circuit boards with electronics mounted thereon fordata acquisition, control and communication. Some or all of theelectronics may be mounted with predominantly surface mount connections.One or more of the boards may be potted in place within the sealed spacewith a resin having elastic properties. The circuitry may include apressure sensor mounted inside the sealed space for sensing the internalpressure of the air gun. The circuitry may include a connector on thesolenoid housing which is used to connect to all control and qualitycontrol operations of the air gun. The circuitry may include a waterdepth sensor and a zero-field hydrophone housed within the transducerhousing. The circuitry may include a connection of the air gunelectronics to an air gun string network that allows multiplexedmultiple air guns on a single communications line. The circuitry mayinclude a connection to an external air gun timing sensor mountedoutside the solenoid and attached to the air gun. The circuitry may beconnected to receive signals from the pressure sensor and adapted tomeasure internal air pressure of the air gun. The circuitry may enabledetecting of air leaks from the sealed space. Circuitry may be adaptedto synchronize the air gun based on the internal air gun air pressure.The depth and/or zero-field hydrophone sensor detection may be added orremoved from the air gun without adding additional connectors exposed tothe water. All sensors and actuation control functions for an air gunmay be connected using only one in-water connection at the air gun. Insome aspects, the digital control wires for an air gun are isolated fromthe other air guns in order to improve reliability and fault findingoperations. The air gun may be connected to a digital control network,for example, to reduce the number of wires going to the seismic vessel.The air gun may include a connector or adaptor all types of air gunsusing the optional external air gun timing sensor connection.

These and other aspects may be implemented as methods, systems, devices,computer program products, or otherwise. Some aspects may include and/orutilize instructions tangibly stored on a computer readable mediumand/or instructions tangibly encoded in digital logic. Such instructionsmay be operable to cause a digital electronic controller to perform theoperations and/or functionality described. Digital electroniccontrollers may include digital logic circuitry, digitalmicrocontrollers and/or programmable processors. Some digital electroniccontrollers may run on software, while others may operate independent ofsoftware.

These and other aspects may provide one or more of the followingadvantages. An air gun cluster may be implemented with fewer externalconnectors exposed to the water. A marine air gun may be actuated,synchronized and/or monitored more accurately and/or more reliably. Aseismic source system may be operated with fewer or less frequentelectronic, mechanical, and/or pneumatic errors. Difficulties introubleshooting electronic, mechanical, and/or pneumatic faults may bereduced. Data acquisition may be improved. The internal pressure in thepressure chamber of the pressure release assembly may be detected, whichmay improve leak detection and/or overall control and/or synchronizationof the marine air guns. Air guns, communication links, and/or othercomponents may be more reliably or easily interchangeable. A smallerumbilical may carry the communication links that provide point-to-pointcommunication with each air gun cluster. The air gun array may bedeployed a greater distance from the vessel towing the array. Hardwareand/or processes for digital communications between the air gun and thecommand center may be simplified. The weight and/or drag of varioussystem components may be reduced.

The details of one or more implementations are set forth in theaccompanying drawings and the description below. Other features will beapparent from the description and drawings, and from the claims.

DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram showing an example marine seismic sourcesystem.

FIGS. 2A and 2B are schematic diagrams showing example marine seismicsource systems.

FIGS. 3A and 3B are diagrams showing example air gun clusters.

FIGS. 4A and 4B are diagrams showing an example marine air gun.

FIGS. 4C and 4D are diagrams showing aspects of the example marine airgun 400 of FIGS. 4A and 4B.

FIGS. 5A and 5B are diagrams showing an example marine air gun.

FIG. 5C is a diagram showing aspects of the example marine air gun 500of FIGS. 5A and 5B.

FIGS. 6A and 6B are diagrams showing an example marine air gun.

FIG. 7 is a block diagram showing example electronic components of amarine air gun.

FIGS. 8A and 8B are schematic diagrams showing an example marine airgun.

FIG. 9A is a flow chart showing an example process for operating amarine air gun.

FIG. 9B is a flow chart showing an example process for operating amarine air gun.

FIG. 10A is a block diagram showing example electronic components of amarine air gun.

FIG. 10B is a block diagram showing example electronic components of amarine seismic command center.

FIG. 11 is a block diagram showing an example high voltage supply of amarine air gun.

FIG. 12 is a signaling a flow chart showing an example process foroperating a marine seismic source system.

Like reference symbols in the various drawings indicate like elements.

DETAILED DESCRIPTION

FIG. 1 is a block diagram showing an example marine seismic sourcesystem 100. The example system includes an array 118 of air gunsclusters 120 towed by a vessel 102. Each cluster 120 may include one,two, three, or more marine air guns that generate an acoustic signal inthe water. Different clusters may include different numbers of air guns.For example, some of the clusters 120 may each have a single air gun,while other clusters 120 may each include two or three air guns.

Each air gun houses its own digital electronic control circuitry. Theelectronic circuitry for an air gun may be carried in a sealed chamberdefined by structures integral with the air gun body, structuresattached to the air gun body, structures mounted on the air gun body,structures abutting the air gun body, and/or structures otherwisecarried by the air gun body. In the example system 100, each air gunalso houses transducers (e.g., depth transducers, pressure transducers,hydrophones, etc.) communicably coupled to the air gun's digitalelectronic circuitry. The digital electronic circuitry of each marineair gun can control operation of the marine air gun based on digitalcommunications received from a command center 106, and/or the digitalelectronic circuitry can collect data from the transducers. The digitalelectronic circuitry may digitize the data, store the data, and/ortransmit the digital data back to the command center 106.

In some implementations, a dedicated point-to-point communication linkbetween each marine air gun cluster 120 and the command center 106allows the command center 106 to exchange digital communications witheach marine air gun individually. For example, each marine air gun maytransmit digital data to the command center 106 by modulating current onthe dedicated communication link, and/or the command center 106 maytransmit digital data to each marine air gun by modulating voltage onthe dedicated communication link.

The electronic circuitry embedded in the marine air gun can tolerate theharsh working conditions of the marine air gun. For example, in a someseismic surveys, the marine air gun is submersed in salt water or freshwater, subject to marine turbulence, and jolted by seismic signals fromthe marine air gun. In some instances, the electronic componentsexperience forces over one thousand times the force of gravity when themarine air gun generates the acoustic signal. The robust configurationof the electronics may sustain such conditions for reliable andcontinuous operation through several seismic surveys withoutinterruption. In some cases, all or part of the electronic circuitry areintegrated in one or more circuit boards or similar structures, and theintegrated structure is secured in a chamber of the air gun byshock-absorbing material. The shock-absorbing material may have elasticproperties that reduce wear or damage to the electronic circuitrycomponents. Example shock-absorbing material include gels, epoxies,resins, potting materials, and others.

The electronic circuitry may be spatially compact to allow all or partof the electronic circuitry to be integrated directly into a housing ofthe air gun actuator (e.g., the solenoid valve housing), a sensorhousing (e.g., the pressure transducer housing, etc.), or a differentstructure of the marine air gun. For example, the digital electroniccircuitry can be integrated on a single circuit board that fits in asolenoid housing. By integrating the electronic circuitry into a commonhousing with an actuator or sensor of the marine air gun, the circuitrycan communicably couple to the actuator or sensor without externalconnectors exposed to the water. For example, the electronic circuitrycomponents can be electrically connected to the actuators and sensors ofthe marine air gun by surface-mount soldered connections within a commonsealed chamber, which may reduce the number of external connectors. Inaddition to reducing exposure to water, the surface-mount solderedconnections may provide a mechanically and electrically robust couplingamong the electronic components and/or between the electronic componentsand the other air gun components (e.g., the solenoid, transducers,etc.).

In the example system 100, the vessel 102 tows an array 118 of air gunclusters 120. The vessel 102 includes a navigation center 104, a commandcenter 106, and one or more reels 110. The vessel 102 may include an airsupply (not shown) that provides pressurized air to the air guns in thearray 118. An air supply may include a cylinder or chamber that storegas at high pressure, a pump that pressurize the gas, regulators thatcontrol gas pressure, valves that control gas flow, and/or otherfeatures. The pressurized air provided to the air guns is stored in oneor more chambers in the pressure release assembly of the air gun andreleased by the pressure release assembly to generate the acousticsignal. The pressurized air may also be stored in one or more chambersin an actuator of the air gun and released by the actuator to actuatethe pressure release assembly.

The pressurized or compressed air used by a marine seismic source systemand/or by components of a marine seismic source system may include anytype of compressible fluid. For example, the air supply on the vessel102 may include supplies of helium, nitrogen, oxygen, carbon dioxide,argon, or any combination of these and/or other gases. For example, thecompressed air communicated to the marine air guns and released by themarine air guns to generate the acoustic signal may include one or moreof these example gases in any ratio or combination. Some marine air gunsmay also generate an acoustic signal by releasing non-compressiblefluid. For example, in some instances a marine air gun releases water togenerate an acoustic signal in water.

The vessel 102 may include a power supply that generates electricalpower for operating one or more components of the system 100. A powersupply may include a DC voltage supply that provides a constant voltage,an AC voltage supply that provides a time-varying voltage, and/or othertypes of power supply. The vessel 102 may include additional and/ordifferent features. In some implementations, the system 100 operates inaccordance with one or more operations of the process 1200 shown in FIG.12. In some implementations, the system 100 operates in a differentmanner.

Each air gun cluster 120 is coupled to an umbilical 112 extending fromthe reels 110. The umbilical 112 includes communication links supportingcommunications between the command center 106 and the air guns at eachclusters 120. Each umbilical 112 includes a bell housing 114. The bellhousing 114 may include a multiplexer that multiplexes and/ordemultiplexes communications to and/or from the command center 106. Themultiplexer may be mounted internal to the bell housing 114, external tothe bell housing 114, and/or in another location.

The navigation center 104 navigates the vessel 102. The navigationcenter 104 may navigate the vessel 102 based on automated and/or manualcontrol. For example, the navigation center 104 may be programmed toguide the vessel 102 through a trajectory specified for one or moreseismic surveys. During a seismic survey, the navigation center 104 maynavigate based on data stored locally on the vessel 102, based on globalpositioning system (GPS) data received by the vessel 102, based on datareceived wirelessly (e.g., via satellite, via radio frequencytransmission, and/or another medium) from a remote location, and/orbased on other types of information.

The navigation center 104 may communicate with the command center 106.For example, the navigation center 104 may send the command center 106instructions to fire the air gun array 118, and/or the command center106 may send the navigation center 104 information relating to thestatus of the air gun array 118 (e.g., location information, firingstatus information, etc.), which may include information relating toindividual clusters 120, information relating to individual air guns inthe array 118, and/or information relating to the array 118 as a whole.

The command center 106 operates the array 118 based on digitalcommunications with the air guns in each cluster 120. The command center106 includes a communication interface 108 that transmits digital datato and receives digital data from the air guns in the array 118. Thecommand center 106 may include additional and/or different features. Thecommand center 106 may include a computer system, for example, thatincludes processors running software for performing some or all of thefunctionality of the command center. The computer system may includememory that can store data received from and/or relating to operationsof the air guns. The computer system may include display devices (e.g.,monitors, etc.) that can display the data in various formats and/or userinterface devices (e.g., keyboard, mouse, etc.) that receive user input.Generally, the command center 106 may receive, store, analyze, generate,and/or transmit data relating to the air gun array 118 and/or datarelating to other aspects of a seismic survey. In some instances, someor all of the command center 106 computing operations and functionalitymay be performed at a remote location. The command center 106 mayinclude a power supply that provides electrical power provided to theair gun array 118. The power supply may supply electrical energy at oneor more voltage levels (e.g., 5 Volts, 10 Volts, 20 Volts, 40 Volts, 80Volts, etc.). The command center 106 may control the level of electricalvoltage and/or power provided to each air gun cluster 120.

The communication interface 108 transmits electrical power and commandsand/or other information to the air gun(s) at each clusters 120. Thecommands may be based on data received from the navigation center 104,data stored or generated locally by the command center 106, datareceived from a remote location (e.g., remote from the vessel 102),and/or other data. The commands sent to the air guns may include varioustypes of instructions for conducting a seismic survey. For example, thecommands may include a fire command, instructions to prepare for a firecommand, commands to reconfigure an air supply valve, requests for data,and/or other types of commands. The commands and/or other informationsent from the communication interface 108 may be addressed to all airguns, to individual air guns, to individual air gun clusters 120, and/orto subsets of air guns. For example, the communication interface 108 mayaddress a command to an individual air gun by transmitting an identifierwith the command (e.g., as a header), where the identifier correspondsto the individual air gun. Each air gun may have a unique identifier.The commands may include digital communications in any digitalcommunication format. For example, the digital communications mayinclude asynchronous digital communications, synchronous digitalcommunications, and/or other formats.

The communication interface 108 receives data and/or other types ofinformation from the air gun(s) at each cluster 120. The data receivedfrom an air gun may include data collected by transducers at the airgun, data generated by a digital controller at the air gun, and/or otherdata. The data received from an air gun may include various types ofdata relating to a seismic survey. For example, the information mayinclude data from a one or more transducers associated with the air gun,data from a GPS receiver associated with the air gun, data relating toan air supply and/or air supply valves, various types of quality controldata, timing signals, ready signals, data requested by the commandcenter 106 and/or other types of data. The information received by thecommunication interface 108 may include an identifier that correspondsto the individual air gun that sent the information. The data receivedby the communication interface may include digital communications in anydigital communication format. For example, the digital communicationsmay include asynchronous digital communications, synchronous digitalcommunications, and/or other formats.

In the example system 100, the reels 110 control the positions of theair gun clusters 120 by controlling the deployed length of eachumbilical 112. The communication links in each umbilical 112 arecommunicably coupled to the communication interface 108. Thecommunication links may be directly coupled to the communicationinterface 108, or the communication links may be indirectly coupled tothe communication interface 108 through a network and/or connectors,which may include one or more communication links.

In some implementations, each umbilical 112 includes a communicationlink for each cluster 120. In the example shown, each umbilical 112 mayinclude eight communication links, where each of the communication linksis communicably coupled to the communication interface 108 and airgun(s) in a cluster 120. Each umbilical 112 may include one or moreadditional communication links. For example, each umbilical may includeone or more backup communication links that can be used fortroubleshooting purposes, backup purposes, supplemental communicationand/or for communications with devices other than the air guns. In theexample system, the communication link for each cluster 120 alsoprovides electrical energy that powers the electronics at the cluster120. In some implementations, each umbilical 112 may include a separatepower link that provides power to the cluster 120 independent ofcommunications. Each umbilical 112 may include an air supply line thatprovides pressurized air from an air supply on the vessel 102 to eachair gun. Each umbilical 112 may include additional and/or differentfeatures. In some cases, the umbilical 112 does not include air supply,and one or more air supply lines run from the vessel 102 to each air guncluster 120 separate from the umbilical 112.

In some implementations, each umbilical 112 includes a multiplexer atthe bell housing 114 and a multiplexed communication link between themultiplexer and the communication interface 108. In suchimplementations, the communication interface 108 may also include amultiplexer that combines communications for multiple air gun clusters120 onto a single multiplexed communication link. The multiplexer at thebell housing 114 on the umbilical 112 can demultiplex the data from themultiplexed link onto the separate communication links for each air guncluster 120. As such, point-to-point communications between the commandcenter 106 and each air gun cluster 120 may include multiplexed linksthat each support communication between the command center 106 andmultiple air gun clusters 120 and dedicated (i.e., non-multiplexed)links that each support communications between the command center and anindividual air gun cluster 120.

FIGS. 2A and 2B are diagrams showing example marine seismic sourcesystems 200 a, 200 b. Although either system 200 a, 200 b may include anarray having several strings of air gun clusters, only a single stringis shown in each of FIGS. 2A and 2B. Three example air gun clusters 214a, 214 b, 214 c are shown, and each air gun cluster is shown as having asingle air gun. Each of the systems 200 a, 200 b may include strings ofair guns having greater or fewer than three clusters, and each clustermay include more than one air gun.

The example system 200 a of FIG. 2A includes dedicated communicationlinks for each air gun cluster. The umbilical 112 a in FIG. 2A includesindividual communication links 212 a, 212 b, 212 c for each air guncluster 214 a, 214 b, 214 c. A first communication link 212 a providescommunications between the command center 106 and the first air guncluster 214 a; a second communication link 212 b provides communicationsbetween the command center 106 and the second air gun cluster 214 b; anda third communication link 212 c provides communications between thecommand center 106 and the second air gun cluster 214 c. Eachcommunication link 212 a, 212 b, 212 c extends from the reel 110 to anair gun cluster. As such, each communication link 212 a, 212 b, 212 cextends through the portion 202 of the umbilical 112 nearest the vessel102 (between the bell housing 114 a and the reel 110), and the bellhousing 114 a does not utilize a multiplexer. In some implementations,each communication link 212 a, 212 b, 212 c extends from the reel 110 tothe command center 106. In some implementations, one or more differentcommunication links 201 (which may or may not include a multiplexedlink) communicably couples the communication links 212 a, 212 b, 212 cto the command center 106 from the reel 110.

The example system 200 b of FIG. 2B also includes dedicatedcommunication links for each air gun cluster. As in FIG. 2A, theumbilical 112 b in FIG. 2B includes individual communication links 212a, 212 b, 212 c for each air gun cluster 214 a, 214 b, 214 c. Theumbilical 112 b in FIG. 2B includes a multiplexed link 204 between thereel 110 and the bell housing 114 b. As such, each communication link212 a, 212 b, 212 c extends only between the bell housing 114 b and oneof the air gun clusters. The bell housing 114 b includes a multiplexerthat performs multiplexing and demultiplexing operations for convertingdata between the dedicated communication links 212 a, 212 b, 212 c andthe multiplexed link 204. In some implementations, multiplexed link 204extends from the reel 110 to the command center 106. In someimplementations, one or more different communication links 201 (whichmay or may not include a multiplexed link) communicably couples themultiplexed link 204 to the command center 106 from the reel 110.

FIGS. 3A and 3B are diagrams showing example air gun clusters. The airgun clusters may be towed by a vessel (not shown). FIG. 3A shows anexample cluster 300 a with two marine air guns 322 a, 322 b. FIG. 3Bshows an example cluster 300 b with one marine air gun 323. In someimplementations, a cluster may include more than two air guns. In someimplementations, each of the clusters 120 of FIG. 1 can be implementedas the cluster 300 a, the cluster 300 b, and/or another type of air guncluster. In some implementations, the systems 200 a, 200 b of FIG. 2 caninclude one or more of the clusters 300 a, 300 b, and/or different typesof air gun clusters.

The cluster 300 a shown in FIG. 3A includes a hanger plate 313 asubmersed in water, the two air guns 322 a, 322 b submersed in water,and a flotation device 330 at the water surface 332. The cluster 300 amay include additional and/or different features. The flotation device330 floats at the water surface 332 and suspends that hanger plate 313a. The hanger plate 313 a suspends the air guns 322 a, 322 b at a depthbelow the hanger plate 313 a. Chains, cables, and/or other suitablestructures may be used to suspend the hanger plate 313 a and/or the airguns 322 a, 322 b at a desired depth. For example, the air guns 322 a,322 b may be deployed at a depth of twenty feet, thirty feet, or anotherdepth below the water surface 332. The components of the cluster 300 amay be arranged in a different configuration. In some instances, the airguns 322 a, 322 b may be suspended from the floatation device 330, andthe hanger plate 313 a can be suspended from the air guns 322 a, 322 bat a depth below the air guns 322 a, 322 b. The air guns 322 a, 322 bmay be suspended at the same depth below the water surface 332 or atdifferent depths.

Two air supply lines 316 extend from a main air supply line 308 to thehanger plate 313 a. Each of the air supply lines 316 extends from thehanger plate 313 a to one of the air guns 322 a, 322 b. The air supplylines 316 provide pressurized air to the air guns. The hanger plate 313a and/or the air guns 322 a, 322 b may include one or more valves (notshown) that control the flow of air through the supply lines 316. Themain air supply line 308 may provide pressurized air to one or moreadditional clusters in an air gun array. The main air supply line 308may receive air from an air supply on a vessel that tows the cluster 300a.

The air guns 322 a, 322 b receive the pressurized air from the airsupply lines 316 and store the air at high pressure in a chamber in theair gun. When actuated by an actuator (e.g., a solenoid valve), apressure release assembly of each air gun 322 a, 322 b can release thecompressed air to generate an acoustic signal in the water. The actuator(e.g., a solenoid valve) of the air guns 322 a, 322 b may also receivethe pressurized air from the air supply lines 316 and store the air athigh pressure in a chamber of the actuator. The actuator can use thecompressed air to pneumatically actuate the pressure release assembly inresponse to an electrical signal (e.g., a voltage signal) received bythe actuator. Digital electronic circuitry housed at each air gun 322 a,322 b may control the electrical signal applied to the actuator of theair gun to control the pressure release. The digital control electronicsat each air gun 322 a, 322 b may control the air gun based on digitalcommunications received from a command center (e.g., the command center106 of FIG. 1).

The cluster 300 a includes several communication links 305, 305 a, 305b, 311, 314 a, 314 b, 315 and others. The communication links 305, 305a, 305 b, 314 a, 314 b, 315 may transmit digital communications from thecommand center to each air gun 322 a, 322 b and/or from each air gun 322a, 322 b to the command center. In the example shown, each of thecommunication links 305, 305 a, 305 b, 311, 314 a, 314 b, 315, isimplemented as a single twisted pair. A twisted pair includes a pair ofconducting wires that are twisted around each other along all or part ofthe length of the conducting wires. Additional and/or different types ofcommunication link may be used. For example, one or more of thecommunication links 305, 305 a, 305 b, 311, 314 a, 314 b, 315 mayinclude one or more twisted pairs, fiber optic cables, coaxial cables,and/or different types of communication links.

The communication link 305 provides power and communications to thecluster 300 a and transmits data from the cluster 300 a. Thecommunication link 305 extends to the hanger plate 313 a from anumbilical 301. The umbilical 301 extends to one or more additionalclusters in an air gun array. In addition to the communication link 305,the umbilical 301 includes additional communication links that providepower and communications to the other clusters in an air gun array. Eachadditional communication link in the umbilical 301 may be implementedwith a twisted pair and/or with additional or different types ofcommunication links. The umbilical 301 may extend to a vessel that towsthe cluster 300 a and/or to a bell housing towed behind the vessel.

The hanger plate 313 a includes a splitter 304. The splitter 304 splitsthe signal from the communication link 305 into two communication links305 a, 305 b. The communication links 305 a, 305 b may each receiveidentical signals from the communication link 305 through the splitter304. When the air guns 322 a, 322 b transmit data, the splitter 304transfers signals from the communication links 305 a, 305 b to thecommunication link 305. The communication links 305 a, 305 b arecommunicably coupled (e.g., by a connector or another type of coupling)to the communication links 314 a, 314 b, which each extend through thewater to one of the air guns 322 a, 322 b. The cluster 300 a may includeadditional, different, or fewer communication links. For example, insome implementations, the communication links 305 a, 305 b may extendthrough the water to the air guns 322 a, 322 b without coupling tocommunication links 314 a, 314 b.

The air gun 322 a houses digital electronic circuitry communicablycoupled to the communication link 314 a, and the air gun 322 b housesdigital electronic circuitry communicably coupled to the communicationlink 314 b. The digital electronic circuitry in each air gun 322 a, 322b may be housed in a structure that is integral with, mounted on, and/orotherwise carried by the pressure release assembly of the air gun. Thedigital electronic circuitry at each air gun 322 a, 322 b may controloperation of the air gun, for example, by electrically controlling anmechanical or pneumatic actuator that actuates the pressure releaseassembly. The digital electronic circuitry at each air gun 322 a, 322 bmay control operation of the air gun based on digital communicationsreceived at the air gun from the command center (e.g., the commandcenter 106 of FIG. 1).

Each air gun 322 a, 322 b may also house transducers communicablycoupled to the digital electronic circuitry communicably in the air gun.The transducers in each air gun 322 a, 322 b may be housed in astructure that is integral with, mounted on, and/or otherwise carried bythe pressure release assembly of the air gun. The transducers mayinclude pressure transducers, depth transducers, a zero-fieldhydrophone, and/or other types of transducers. The transducers maygenerate electrical signals based on detecting mechanical, acoustic,pneumatic, and/or other types of conditions in or about the air gun. Thetransducers may transmit analog data to the digital electronic circuitryhoused at the air gun, and the digital electronic circuitry may digitizeand store the data. The digital electronic circuitry in the air guns maytransmit the digitized transducer data to the command center through therespective communication links 314 a, 314 b, 305 a, 305 b, and 305.

Each air gun 322 a, 322 b includes connectors that couple to thecommunication links and to the pressurized air supply lines. Theconnectors may include electrical couplings, optical couplings,mechanical couplings, pneumatic couplings, and/or other types ofcouplings. For example, the connectors may include bolts, screws,threading, and/or other types of fasteners that mechanically secure anexternal cable, wire, tube, conduit, or other type of structure to theconnector. As another example, the connectors may include copper and/orother types of metallic fittings that provide conductive coupling forpower and/or communications. As another example, the connectors mayinclude sealed pneumatic fittings for the pressurized air supply line.

The hanger plate 313 a includes a near field hydrophone 310. Thenear-field hydrophone 310 collects acoustic data. The near-fieldhydrophone may be positioned equidistant (or substantially equidistant)from the two air guns 322 a, 322 b, such that when the air guns 322 a,322 b are fired they appear acoustically to the near-field hydrophone310 as a point source. The near-field hydrophone 310 includes anacoustic transducer that converts acoustic signals to electricalsignals. In the example shown, the near-field hydrophone 310 iscommunicably coupled to the digital electronic circuitry in the air gun322 a by a first communication link 311 in the hanger plate 313 a and asecond communication link 315 that extends between the hanger plate 313a and the air gun 322 a. The near-field hydrophone 310 may transmitanalog data to the air gun over the communication links 311, 315, andthe digital electronic circuitry in the air gun 322 a may digitize andstore the data from the near-field hydrophone 310. The digitalelectronic circuitry in the air gun 322 a may transmit the digitizednear-field hydrophone data to the command center through thecommunication links 314 a, 305 a, and 305. Data from the near-fieldhydrophone 310 may be useful for data analysis, quality control, and/ortrouble shooting. For example, data from the near-field hydrophone 310may indicate the magnitude, frequency, duration, timing, and/or otherproperties of the seismic signal generated by the cluster 300 a. In someinstances, data from the near-field hydrophone 310 may be used to detectair leaks in the supply lines and/or in the air guns in the cluster 300a.

In addition to the near-field hydrophone 310, the hanger plate 313 aand/or a different structure in the cluster 300 a may include auxiliarydevices that receive power and/or communications from the communicationlink 305. For example, the cluster 300 a may include a GPS device, airsupply valves, and/or other types of auxiliary devices that receivepower and/or communications from the communication link 305.

The cluster 300 b shown in FIG. 3B includes a hanger plate 313 bsubmersed in water, the air guns 323 submersed in water, and a flotationdevice 330 at the water surface 332. The cluster 300 b may includeadditional and/or different features. The flotation device 330 floats atthe water surface 332 and suspends that hangar plate 313 b. The hangerplate 313 b suspends the air gun 323 at a depth below the hanger plate313 b. Chains, cables, and/or other suitable structures may be used tosuspend the hanger plate 313 b and/or the air gun 323. The components ofthe cluster 300 a may be arranged in a different configuration. In someinstances, the air gun 323 may be suspended from the floatation device330, and the hanger plate 313 b can be suspended from the air gun 323 ata depth below the air gun 323.

An air supply line 318 extends from the main air supply line 308 to thehanger plate 313 b and from the hanger plate 313 b to the air gun 323.The air supply line 318 provides pressurized air to the air gun 323. Thehanger plate 313 b and/or the air gun 323 may include one or more valves(not shown) that control the flow of air through the supply line 318.The air gun 323 may be configured and/or operate in the same manner asthe air gun 322 a of the cluster 300 a in FIG. 3A. For example, the airgun 323 can receive the pressurized air from the air supply line 318,store the air at high pressure in a chamber in the air gun 323, andrelease the compressed air to generate an acoustic signal in the water.The air gun 323 may include the same actuator, digital electronics, andtransducers as the air gun 322 a in FIG. 3A, which may operate asdescribed with respect to the air gun 322 a.

The cluster 300 b includes several communication links 307, 317 a, 317b, and others. The communication links 307 and 317 a may transmitdigital communications from the command center to the air gun 323 and/orfrom the air gun 323 to the command center. In the example shown, eachof the communication links 307, 317 a, 317 b is implemented as a singletwisted pair. Additional and/or different types of communication linkmay be used. The communication link 307 provides power andcommunications to the cluster 300 b and transmits data from the cluster300 b. The communication link 307 extends to the hanger plate 313 b froman umbilical 301.

The hanger plate 313 b may include a splitter 304. The communicationlink 306 is communicably coupled (e.g., by a connector or another typeof coupling) to the communication link 317 a, which extends through thewater to the air gun 323. The cluster 300 b may include additional,different, or fewer communication links. For example, in someimplementations, the communication link 307 may extend through the waterto the air gun 323 without coupling to communication link 317 a.

The hanger plate 313 b includes a near-field hydrophone 309. Thenear-field hydrophone 309 may be configured and/or operate as thenear-field hydrophone 310 of FIG. 3A. In the example shown in FIG. 3B,the near-field hydrophone 309 is communicably coupled to the digitalelectronic circuitry in the air gun 323 by a first communication link312 in the hanger plate 313 b and a second communication link 317 b thatextends between the hanger plate 313 b and the air gun 323. The digitalelectronic circuitry in the air gun 323 may receive analog data from thenear-field hydrophone 309, digitize the data, store the digitized data,and transmit the digitized data to the command center through thecommunication links 317 a, 307.

FIGS. 4A and 4B are diagrams showing an example marine air gun 400. Insome implementations, the marine air guns 322 a, 322 b of FIG. 3A and/orthe marine air gun 323 of FIG. 3B may be implemented as the marine airgun 400. The marine air gun 400 includes a pressure release assembly 404and a control housing 402 carried on the end of the pressure releaseassembly 404. The pressure release assembly 404 includes a housing 405that defines ports 406. Within the housing 405, the pressure releaseassembly 404 defines a pressure chamber that stores compressed air. Thepressure release assembly 404 includes a partition that prevents fluidcommunication between the pressure chamber and the ports 406. Thepartition is moveable to permit fluid communication between the pressurechamber and the ports 406. The partition may be part of a valve, apiston, or another type of structure that moves the partition when thepressure release assembly is actuated. The surge of compressed fluidfrom the pressure chamber through the ports 510 generates an acousticsignal that propagates through the water. FIGS. 8A and 8B show featuresof an example pressure release assembly. The pressure release assembly404 may include features that are the same as or similar to the featuresof the example pressure release assembly 802 of FIGS. 8A and 8B. The airgun 400 may include a different type of pressure release assembly, forexample, that includes different features and/or operates in a differentmanner than the pressure release assembly 802 of FIGS. 8A and 8B.

FIG. 4C is a perspective view of the end of the air gun 400 that carriesthe control housing 402, and FIG. 4D is an exploded view of the controlhousing 402. The control housing 402 may be integral with the housing405 and/or another component of the pressure release assembly 404. Thecontrol housing 402 may be a separate structure from the pressurerelease assembly 404. The control housing 402 may be bolted, welded, orotherwise mechanically attached to the housing 405 and/or anothercomponent of the pressure release assembly 404. The control housing 402includes a cap plate 420 that can be bolted or otherwise secured to abody of the control housing 402. The control housing 402 may be modifiedand/or adapted for different types of pressure release assemblies. Thecontrol housing 402 may be modified for different types of communicationinterfaces, air supply lines, power supply sources, and/or otherfeatures external to the air gun 400.

The control housing 402 includes connectors that couple the air gun 400to one or more communication links, one or more power supplies, one ormore pressurized air supplies, and/or other resources. The controlhousing 402 includes a communication link connector 410 that couples theair gun 400 to a communication link external to the air gun 400. Forexample, the communication link connector 410 may couple to thecommunication link 315 of FIG. 3A, to one or both of the communicationlinks 314 a, 314 b of FIG. 3A, to one or both of the communication links317 a, 317 b of FIG. 3B, and/or to another type of communication link.The communication link connector 410 may communicably couple theexternal communication link to digital electronic circuitry in thecontrol housing 402. For example, the communication link connector 410may communicably couple an external communication link to acommunication interface and/or a digital electronic controller in thecontrol housing. As another example, the communication link connector410 may communicably couple an external communication link to one ormore power supply modules in the control housing 402. In the exampleshown, the communication link connector 410 provides all externalelectrical connections for the air gun 400 in a single externalconnector. In some implementations, additional external connectors maybe used.

The control housing 402 includes a pressurized air supply connector 412that couples the air gun 400 to a pressurized air supply external to theair gun 400. For example, the air supply connector 412 may couple to oneof the supply lines 316 of FIG. 3A, the supply line 318 of FIG. 3B,and/or another type of air supply line. The air supply connector 412 mayprovide pressurized air to the pressure release assembly 404, to anactuator in the control housing 402, and/or to other components of theair gun 400.

The control housing 402 includes a pressure sensor 414 and a depthsensor 418. In the example shown, the pressure sensor 414 abuts thepressure release assembly 404. The pressure sensor 414 may bepneumatically coupled to a pressure chamber in the pressure releaseassembly 404, which may allow the pressure sensor 414 to monitor theinternal pressure of the air gun 400. For example, the pressure sensor414 can measure the internal pressure in the pressure chamber of thepressure release assembly 404. The pressure sensor 414 may monitor theinternal pressure while the air gun 400 fires and/or while the chamberpressurizes before and/or after the air gun 400 fires. The pressuresensor 414 includes a transducer that converts pressure to electricalsignals. Analog data from the pressure sensor 414 can be digitized,stored, and/or transmitted from the air gun 400 by digital electroniccircuitry on the control board 422. Information from the pressure sensor414 may be useful for data analysis, quality control, and/or troubleshooting. Such information may indicate the magnitude, frequency,duration, timing, and/or other properties of the seismic signalgenerated by the cluster 300 a. For example, the pressure sensor 414 mayprovide data relating to when and/or how fast the pressure releaseassembly 404 releases the compressed air to generate the acousticsignal. Such data may be used to synchronize the air gun 400 with otherair guns in an array. The pressure sensor 414 may provide data relatingto the rate at which pressure builds in the pressure chamber. Such datamay be used to diagnose air leaks and/or other problems that may occurduring a marine seismic survey.

The control housing 402 includes a depth sensor 418 and a test airconnector 416 for the depth sensor 418. The depth sensor 418 can detectthe depth of the air gun 400 beneath the water surface. The depth sensor418 includes a transducer that detects depth. For example, depth sensor418 may include a pressure transducer that detects a pressuredifferential between the depth sensor 418 and the water surface, andconverts the pressure differential to an electric signal. Analog datafrom the pressure sensor 414 can be digitized, stored, and/ortransmitted from the air gun 400 by digital electronic circuitry on thecontrol board 422. Data from the depth sensor 418 can be useful forseismic data analysis. For example, the depth sensor 418 may helpidentify the location of the air gun 400 when the air gun 400 is fired.The location of the air gun 400 when it fires indicates the origin ofthe seismic signal generated by the air gun 400, which may be used forprocessing the collected seismic data.

The control housing 402 may also include a zero-field hydrophone (notshown). The zero-field hydrophone may collect acoustic data in theimmediate vicinity of the air gun 400. For example, the zero-fieldhydrophone may be attached to the air gun 400 and/or otherwise carriedby the air gun 400. Data from the zero-field hydrophone may be collectedin addition to or instead of data from a near-field hydrophone that isspaced apart from the air gun 400. Analog data from the pressure sensor414 can be digitized, stored, and/or transmitted from the air gun 400 bydigital electronic circuitry on the control board 422. Data from thezero-field hydrophone may be useful for data analysis, quality control,and/or trouble shooting. For example, data from the zero-fieldhydrophone 310 may indicate the magnitude, frequency, duration, timing,and/or other properties of the seismic signal generated by the air gun400. In some instances, data from the zero-field hydrophone may be usedto detect air leaks and/or other problems that may occur during a marineseismic survey.

The control housing 402 defines a cavity 428 for an actuator thatactuates the pressure release assembly 404. The actuator may beinitiated by an electrical signal applied to the actuator. The actuatormay move in response to the electrical signal, and movement of theactuator may mechanically and/or pneumatically actuate the pressurerelease assembly 404. In the example shown, the actuator in the cavity428 is a solenoid valve 424. The solenoid valve 424 may be a pressurebalanced solenoid valve, an inertial solenoid valve, a combination ofthese, and/or another type of solenoid valve. FIGS. 8A and 8B showfeatures of an example solenoid valve 822. The solenoid valve 424 mayinclude features that are the same as or similar to the features of theexample solenoid valve 822 of FIGS. 8A and 8B. The air gun 400 mayinclude a different type of actuator, for example, that includesdifferent features and/or operates in a different manner than thesolenoid valve 822 of FIGS. 8A and 8B.

The control housing defines a cavity 426 for the electronics thatcontrol the air gun 400. The cavity 426 may be separate from orconnected to the cavity 428. The cavities 426, 428, may form one or moresealed chambers in the control housing 402. Some or all of theelectronics may be mounted on a control board 422 housed in the cavity426. One control board 422 is shown in FIG. 4D. The control board can bea PC board and/or a different type of board. In some implementations,all of the electronic circuitry in the control housing 402 are mountedon the single control board 422. In some implementations, additionalcontrol boards may be used. The cavity 426 may also house one or moreelectronic components apart from the control board 422. For example, thecavity 426 may house one or more capacitors that are electricallycoupled to, but not mounted on, the control board 422. The capacitorsmay be part of a high voltage supply that provides electrical power tothe solenoid valve 424 to actuate the pressure release assembly 404. Theelectronic circuitry may include a digital controller, a digitizer, adigital memory, digital logic devices, resistors, inductors, capacitors,and/or other components. FIGS. 7, 10A, 10B, and 11 show examplecomponents and modules of the electronic circuitry that may be housed inthe control housing 402.

The solenoid valve 424, the control board 422, one or more capacitors(not shown) and/or other components may be mounted in the controlhousing 402 to sustain the mechanical jerk, acceleration, and movementof the air gun 400 firing. For example, one or more of the componentsmay be secured in the cavities 426, 428 of the air gun byshock-absorbing material. The shock-absorbing material may reduce wearor damage to the components. Example shock-absorbing materials includegels, epoxies, resins, potting materials, and others. Connections amongthe components within the control housing 402 may be soldered, welded,and/or otherwise mechanically robust connections. For example, a digitalelectronic processor may be communicably coupled to power supplies, acommunication interface, and/or other components by soldered connectionsin a sealed chamber with the components. As another example, a powersupply may be electrically coupled with the solenoid valve 424 by asoldered connection in a sealed chamber with the power supply and thesolenoid valve 424. Soldered connections in a sealed chamber with thecomponents that they connect may reduce the likelihood of wear orfailure due to water exposure and/or mechanical stress and movement.

In some implementations, some or all of the electronic circuitry of theair gun 400 are carried by the air gun 400 outside of the controlhousing 402. For example, some or all of the electronic components mayreside in a different housing that is integral with, attached to,mounted on, and/or otherwise carried by the pressure release assembly404. FIGS. 6A and 6B are diagrams showing an example marine air gun 600that includes the pressure release assembly 404, an actuator housing604, and a separate controller housing 602. The actuator housing 604 andthe controller housing 602 are both carried by the housing 405 of thepressure release assembly 404 in FIGS. 6A and 6B. The controller housing602 is mounted to the actuator housing 604. For example, the controllerhousing 602 may be a separate structure mounted to the actuator housing604 by a bolted, welded, or other type of mechanically robust mount. Thecontroller housing 602 and the actuator housing 604 may each containshock-absorbing material to protect the components in the housing. Eachhousing may define a sealed chamber that contains electrical and/ormechanical components that control operation of the air gun 600, andeach housing may include soldered connections among the components.

Together, the controller housing 602 and the actuator housing 604include the components of the control housing 402 of FIGS. 4A, 4B, 4C,and 4D. For example, the controller housing 602 may house some of theelectronic circuitry contained in the cavity 426 of the control housing402 shown in FIG. 4D, and the actuator housing 604 may house theactuator contained in the cavity 428 of the control housing 402 shown inFIG. 4D.

FIGS. 5A and 5B are diagrams showing an example marine air gun 500. FIG.5C is a perspective view of an end of the air gun 500. In someimplementations, the marine air guns 322 a, 322 b of FIG. 3A and/or themarine air gun 323 of FIG. 3B may be implemented as the marine air gun500. The marine air gun 500 includes a pressure release assembly 506 andthree housings carried on the end of the pressure release assembly 506.As shown in FIG. 5A, the actuator housing 502 and the timing sensorhousing 511 are each mounted on the housing 505 of the pressure releaseassembly 506, and the controller housing 504 is mounted on the actuatorhousing 502. In some implementations, one or more of the housings may beintegral with another housing or structure of the air gun 500. Eachhousing may be a separate structure mounted to another housing by abolted, welded, or other type of mechanically robust mount. Each housingmay contain shock-absorbing material to protect the components in thehousing from impact. Each housing may include soldered connections amongcomponents in the housing. Each housing may define a sealed chamber thatcontains electrical and/or mechanical components that control operationof the air gun 500.

The pressure release assembly 506 includes a housing 505 that definesports 510. Within the housing 505, the pressure release assembly 506defines a pressure chamber that stores compressed air. The pressurerelease assembly 506 includes a partition that prevents fluidcommunication between the pressure chamber and the ports 510. Thepartition is moveable to permit fluid communication between the pressurechamber and the ports 510. The surge of compressed fluid from thepressure chamber through the ports 510 generates an acoustic signal thatpropagates through the water.

The actuator housing 502 carries an actuator. For example, the actuatorhousing 502 may house a solenoid valve that actuates the pressurerelease assembly 506. The actuator housing 502 includes a communicationlink connector. The controller housing 504 houses the electroniccircuitry. For example, the controller housing 504 may house a digitalelectronic controller, a memory, a communication interface, and/or otherelectronic components. FIGS. 7, 10A, 10B, and 11 show example componentsand modules of the electronic circuitry that may be housed in thecontroller housing 504. The controller housing 504 also includes a depthtransducer 503 with an air supply fitting.

The timing sensor housing 511 houses a sensor that detects a pressurerelease event by the pressure release assembly 506. For example, thetiming sensor housing 511 may include a pressure transducer that detectsa change in pressure in or about the pressure release assembly 506, forexample, when the pressure release assembly generates the acousticsignal. Data relating to the pressure release event may be digitized,stored, and/or transmitted by the digital electronic circuitry in theactuator housing and the controller housing 504. The timing of thepressure-release event may be analyzed to synchronize the firing of theair gun 500 with other air guns in the array. In the example shown, aconnector on the timing sensor housing 511 is coupled to a connector onthe actuator housing 502 by an external communication link 508. The link508 may provide power and/or data communications between the componentsin the timing sensor housing 511 and the actuator housing 502.

FIG. 7 is a block diagram schematically illustrating example electronicmodules 700 of a marine air gun. The electronic modules 700 include apower and communications module 702, a communication interface module704, a low voltage supply module 706, a high voltage supply module 708,a digital electronic controller module 710, an actuator interface module712, and transducer interface modules 716 a, 716 b, 716 c. The actuatorinterface module 712 is communicably coupled to an actuator 714. Eachtransducer interface module 716 a, 716 b, 716 c is communicably coupledto a transducer 718 a, 718 b, 718 c as shown. The electronic modules 700of a marine air gun may include fewer, additional and/or differentcomponents. The electronic modules 700 may all be housed in a commonhousing, or one or more of the electronic modules 700 may be housed inseparate housings. For example, some or all of the electronic modules700 may be included in the electronic circuitry 820 in the controlhousing 801 of the air gun 800 in FIGS. 8A and 8B. One or more of theelectronic modules 700 may be mounted on a circuit board carried by theair gun. For example, in some implementations, one or more of theelectronic modules 700 are installed on the control board 422 of FIG.4D. In some implementations, the electronic modules 700 are installed onmultiple circuit boards and/or other structures.

Each of the electronic modules 702, 704, 706, 708, 710, 712, 716 a, 716b, 716 c may include digital electronic circuitry. Digital electroniccircuitry may include, for example, filters, digital logic gates (e.g.,AND, OR, NAND, NOR, XOR, etc.), operational amplifiers, transistors,diodes, resistors, capacitors, and/or other components. One or more ofthe components may include analog electronic circuitry. Generally,connections among the electronic modules 700 and/or within eachelectronic module 702, 704, 706, 708, 710, 712, 716 a, 716 b, 716 c mayinclude any suitable electrical and/or mechanical couplings. Conductorsmay be electrically coupled by crimped, soldered, threaded, woven,pin-and-socket, and/or any other suitable type of couplings. In someinstances, components in a common sealed chamber are connected bysurface-mount soldered connections. In some instances, components inseparate housings are coupled by internal or external links, which mayinclude insulated wires, connectors, and/or other features. The inputsignals and output signals of each of the electronic modules 702, 704,706, 708, 710, 712, 716 a, 716 b, 716 c may include digital and/oranalog signals. FIG. 10A shows features of an example implementation ofthe power and communications module 702, the communication interfacemodule 704, and the digital electronic controller module 710. FIG. 11shows features of an example implementation of the high voltage supplymodule 708.

The power and communications module 702 communicably couples theelectronic modules 700 to an external system, subsystem, device, ormodule. For example, the power and communications module 702 may becoupled to an external communication link (e.g., the communication links314 a, 314 b, 315, 317 a, 317 b of FIGS. 3A, 3B, and/or others) througha communication link connector (e.g., the communication link connector410 of FIGS. 4C, 4D, and/or others). In some implementations, the powerand communications module 702 is communicably coupled to the externalsystem, subsystem, device, or module through a twisted pair. Additionaland/or different communication links may be used. The externalcommunication link may be communicably coupled to a command center foran air gun array (e.g., the command center 106 of FIG. 1).

The power and communications module 702 may receive power andcommunications from an external link, and provide the received powerand/or communications to other electronic modules in the air gun. Forexample, the power and communications module 702 may receive a constantor time-varying voltage signal from the external link, and the power andcommunications module 702 may provide output to the communicationinterface module 704, the low voltage supply module 706, and/or the highvoltage supply module 708 based on the voltage signal. The power andcommunications module 702 may also receive input from one or more of theelectronic modules 700 of the air gun. For example, the power andcommunications module 702 may receive digital communications from thecommunication interface module 704 and transmit the receivedcommunications over an external link. As another example, the power andcommunications module 702 may receive power from the low voltage supplymodule 706 and use the power for operating components of the power andcommunications module 702.

The power and communications module 702 may provide the same outputsignal to each of the modules 704, 706, 708. For example, the power andcommunications module 702 may receive an input signal from an externalcommunication link and split the input signal among the modules 704,706, 708. The power and communications module 702 may provide differentoutput signals to each module. For example, the power and communicationsmodule 702 may condition and/or modify the input signal and provide theconditioned and/or modified signal to one or more of the modules 704,706, 708. In some implementations, the power and communications module702 may filter, amplify, rectify, combine, superpose and/or otherwisecondition or modify the signal for one or more of the modules 704, 706,708.

The communication interface module 704 may receive input signals fromthe power and communications module 702. For example, the input signalsmay include digital communications received by the power andcommunications module 702 from an external communication link. Thecommunication interface module 704 can convert the input signals tooutput signals suitable for the digital electronic controller module710. For example, communication interface module 704 may convert inputdigital communication signals to binary voltage signals. In someimplementations, a binary voltage signal is a voltage signal in one oftwo voltage ranges. For example, a low voltage range may be zero Voltsto two Volts, and a high voltage range may be three Volts to five Volts.Different low and/or high voltage ranges may be used. The binary voltagesignals may represent binary data. For example, a binary voltage signalin a low voltage range may represent logical 0, and a binary voltagesignal in a high voltage range may represent logical 1. A binary voltagesignal may be converted and/or stored in a bit of binary memory. In theexample communication interface module 704 in FIG. 10A, a comparator1012 converts the input voltage signals from a pair of conductors tobinary voltage signals. In some implementations, the communicationinterface module 704 generates binary voltage signals in a differentmanner.

The communication interface module 704 may receive input signals fromthe digital electronic controller module 710. For example, the inputsignals may include digital communications for transmission to a commandcenter over an external communication link. The input signals from theelectronic controller module 710 may be formatted as binary voltagesignals. The communication interface module 704 can convert the inputsignals to output signals suitable for transmission to an externalsystem, subsystem, device, or module through the power andcommunications module 702. For example, the output signals may includecurrent modulations, voltage modulations, and/or other types of signalsthat can be detected on the communication link by a command center. Inthe example communication interface module 704 in FIG. 10A, a transistor1008 converts the input signals from binary voltage signals to currentmodulations. In some implementations, the communication interface module704 generates current modulations in a different manner.

The low voltage supply module 706 receives input signals from the powerand communications module 702. The input signal may include a rectifiedtime-constant signal (e.g., direct current). The input signal mayinclude a time-varying signal (e.g., alternating current). The lowvoltage supply module 706 may include a rectifier module that converts atime-varying signal to a time-constant signal. The low voltage supplymodule 706 may include additional filters, amplifiers, and/or othercomponents. The low voltage supply module 706 may store power receivedfrom the power and communications module 702. For example, the lowvoltage supply module 706 may store the power in capacitor, batteries,and/or other suitable components. The low voltage supply module 706 canprovide output power to one or more of the electronic modules, one ormore of the transducers, and/or other devices and components. (Outputconnections of the low voltage supply module 706 are not shown in FIG. 7for clarity.) The output from the low voltage supply module 706 may be atime-constant signal (e.g., direct current) or a time-varying signal(e.g., alternating current). The output from the low voltage supplymodule 706 may be include one or more voltage levels (e.g., 3.3 Volts, 5Volts, and/or another voltage level).

The high voltage supply module 708 receives input signals from the powerand communications module 702. The input signal may include a rectifiedtime-constant signal (e.g., direct current). The input signal mayinclude a time-varying signal (e.g., alternating current). The highvoltage supply module 708 may include a rectifier that converts atime-varying signal to a time-constant signal. The high voltage supplymodule 708 may include additional filters, amplifiers, and/or othercomponents. The high voltage supply module 708 may store power receivedfrom the power and communications module 702. For example, the highvoltage supply module 708 may store the power in capacitor, batteries,and/or other suitable components. The high voltage supply module 708 canprovide output power to the actuator 714 through the actuator interfacemodule 712. The output from the high voltage supply module 708 may beinclude one or more voltage levels (e.g., 40 Volts, 80 Volts, and/oranother voltage level).

The digital electronic controller module 710 can control one or moreaspects of operation of the air gun. In the example shown, the digitalelectronic controller module 710 controls the electrical signal appliedto the actuator 714 from the high voltage supply module 708. The digitalelectronic controller module 710 controls the electrical signal appliedto the actuator 714 by controlling the state of the actuator interfacemodule 712. The actuator interface module 712 can be a switch that canbe turned on or off by the digital electronic controller module 710. Forexample, the actuator interface module 712 may include a transistor(e.g., a field effect transistor, a bipolar junction transistor, oranother type of transistor) that has a conducting state and anon-conducting state. In some implementations, the digital electroniccontroller module 710 can apply a first binary voltage signal to thetransistor to electrically couple the high voltage supply module 708 tothe actuator 714, and the digital electronic controller module 710 canapply a second binary voltage signal to the transistor to electricallyuncouple the high voltage supply module 708 and the actuator 714. Inresponse to the electrical signal from the high voltage supply module708, the actuator 714 may move to actuate a pressure release assembly ofthe air gun. For example, the actuator 714 may be the solenoid valve 424of FIG. 4D, the solenoid valve 822 of FIGS. 8A and 8B, and/or anothertype of actuator. The electrical signal applied to the actuator 714 toactuate the pressure release assembly of the air gun may be, forexample, 40 Volts, 80 Volts, or another voltage level.

The digital electronic controller module 710 may also control operationof the transducers 718 a, 718 b, 718 c by controlling the transducerinterface modules 716 a, 716 b, 716 c. For example, the transducerinterface modules 716 a, 716 b, 716 c may include one or more switches(e.g., transistors and/or other types of electrically-controlledswitches) controlled by the digital electronic controller module 710.The digital electronic controller module 710 may apply a binary voltagesignal or another type of signal to the appropriate transducer interfacemodule 716 a, 716 b, 716 c to couple the digital electronic controllermodule 710 to the corresponding transducer 718 a, 718 b, 718 c. Each ofthe transducers 718 a, 718 b, 718 c may send analog data to the digitalelectronic controller module 710 through its respective transducerinterface module 716 a, 716 b, 716 c. The digital electronic controllermodule 710 may include a digitizer that digitizes the data from thetransducers 718 a, 718 b, 718 c. The digital electronic controllermodule 710 may include a digitizer (e.g., and analog-to-digitalconverter) that digitizes the data from the transducers 718 a, 718 b,718 c. The data may be digitized, for example, at 1 kHz, 10 kHz, 100kHz, or a different frequency. The digital electronic controller module710 may include a memory (e.g., a register, or another type of digitallogic device) that stores the data from the transducers 718 a, 718 b,718 c. The transducers 718 a, 718 b, 718 c may include a pressuretransducer, a depth transducer, a zero-field hydrophone, and/or othertypes of transducers housed at the air gun. The transducers 718 a, 718b, 718 c may include a near-field hydrophone and/or other types oftransducers housed apart from the air gun. Three transducers andtransducer interface modules are shown in the example of FIG. 7. An airgun may include, and the digital electronic controller module 710 may becoupled to, less than or more than three transducers. In someimplementations, one or more of the transducers detects the currentreceived by the actuator (e.g., the solenoid valve) that actuates thepressure release assembly of the air gun.

The digital electronic controller module 710 may control operation ofthe communication interface module 704. For example, the digitalelectronic controller module may send digital communications to thecommunication interface module 704, and the communication interfacemodule 704 may transmit the digital communications to an externalcommunication link. The digital communications sent to the communicationinterface module 704 from the digital electronic controller module 710may include data stored in a memory of the digital electronic controllermodule 710. The stored data may include digital data based on signalsreceived from the transducers 718 a, 718 b, 718 c and/or other data. Thedigital communications sent to the communication interface module 704from the digital electronic controller module 710 may include thecollected data message 1224 shown in FIG. 12 and/or other messages. Thedigital electronic controller module 710 may receive communications fromthe communication interface module 704. The communications received fromthe communication interface module 704 may include digitalcommunications. The communications received from the communicationinterface module 704 by the digital electronic controller module 710 mayinclude the arm message 1212, the fire command 1216, and/or thecollected data message 1224 shown in FIG. 12 and/or other messages. Insome instances, the digital electronic controller module 710 may receivecommunications directly from the power and communications module 702and/or other electronic modules.

In an example implementation, the digital electronic controller module710 includes a microcontroller manufactured by Microchip. An examplemicrocontroller manufactured by Microchip that may be used to implementsome or all aspects of the digital electronic controller module 710 isMicrochip model number PIC24FJ64GA002. This example microcontrollerincludes 16 bit architecture, 16 MIPS CPU speed, flash memory, 64kilobytes of program memory, 8192 bytes of RAM, an operating voltage of2 to 3.6 Volts, digitizers, internal oscillators, and other features.The microcontroller may perform some or all of the describedfunctionality of the digital electronic controller module 710. In somecases, the digital electronic controller module 710 includes additionaland/or other components that perform the described functionality. Forexample, in addition to or instead of a microcontroller, the digitalelectronic controller module 710 may include a digitizer, a memory, aprogrammable processor, additional microcontrollers, a register, a statemachine and/or additional or different digital electronic components.

Some of the functional operations described in this specification, whichmay include some or all of the functional operations of the digitalelectronic controller module 710, can be implemented in software,firmware, and/or hardware, including the structural means disclosed inthis specification and structural equivalents thereof, or incombinations of them. Such functional operations can be implemented asinstructions tangibly embodied in a computer-readable medium and/or indigital logic. Such instructions (also known as a program, code, orlogic) can be executed by, or may control the operation of, a digitalelectronic controller. Such digital electronic controllers may includedigital logic circuitry, microcontrollers, programmable processors,and/or others. The instructions can be written or encoded in any form ofcode, logic, or program language including compiled, executable,interpreted, assembly, machine, or custom language codes. Suchinstructions can be deployed in any form, including as a module, device,circuit, component, subroutine, file, sub-file, or other unit, which maybe implemented as a standalone, integrated, or embedded system.

Digital electronic controllers may communicate with analog systemsand/or devices by using one or more converters. For example, digitalelectronic controllers may include and/or utilize one or more digitizersthat convert analog signals to digital signals suitable for digitalprocessing, and digital electronic controllers may include and/orutilize one or more digital-to-analog converters that convert digitsignals to analog signals. In some instances, all or part of a digitalelectronic controller may be implemented, for example, as an FPGA (fieldprogrammable gate array), an ASIC (application specific integratedcircuit), and/or other types of devices.

Digital electronic controllers suitable for executing instructionstangibly embodied in a computer-readable medium and/or in digital logicdevices may include programmable processors, microcontrollers, digitallogic circuitry, and/or other types of devices. Such digital electroniccontrollers may store data in a memory and/or receive instructions anddata from a memory. A memory can store binary data in machine-readablemedia, logic, circuitry and/or other configurations. Memory may includerandom access memory, read only memory, mass storage devices, volatilestorage devices, non-volatile storage devices, and/or other types ofmemory. Memory may include magnetic devices, magneto optical devices,optical devices, semiconductor devices, and/or other types of devices.Additionally or alternatively, such digital electronic controllers maysend information to and/or receive information from a communicationinterface, digital and/or analog circuitry, and/or electronic devices.For example, a digital electronic controller may interface with analogsystems (e.g., sensor, controllers, actuators, etc.) through adigitizer. As another example, a digital electronic controller mayinclude and/or utilize a communication interface that converts incomingcommunications to digital signals formatted for the digital electroniccontroller.

FIGS. 8A and 8B are schematic diagrams showing an example marine air gun800. FIG. 8A shows the air gun 800 armed, and FIG. 8B shows the air gun800 fired. Arming the air gun 800 prepares the air gun 800 to fire, andfiring the air gun 800 generates an acoustic signal by releasingpressurized air into the water surrounding the gun 800. The air gun 800includes a pressure release assembly 802 that generates the acousticsignal. The pressure release assembly carries a solenoid valve 822 andelectronic circuitry 820. In the example air gun 800, the solenoid valve822 and electronic circuitry 820 are housed by a control housing 801carried on an end of the pressure release assembly 802. The controlhousing 801 may be integral with, mounted to, and/or otherwise carriedby the pressure release assembly 802. The control housing 801 mayinclude the same and/or similar features as the control housing 402 ofthe air gun 400 in FIGS. 4A, 4B, 4C, and 4D. For example, the controlhousing 801 may house one or more sensors and/or transducers, variousconnectors, and/or different or additional features. The control housing801 may be modified and/or adapted for different types of pressurerelease assemblies and/or to interface with additional and/or differentexternal systems.

The pressure release assembly 802 includes a housing 805 and a piston808. The housing 805 defines chambers 804, 806 and ports 818. Thepressure release assembly 802 includes seals 813, 815, 817 between thehousing 805 and the piston 808. The housing 805 defines a port 803 thatprovides fluid communication between the chamber 804 and the air supplyport 803 in the control housing 801. The housing 805 defines a firingport 807 and a port 809 that provide fluid communication between thechamber 804 and the solenoid valve chamber 832 in the control housing801. The firing port 807 is sealed from the chamber 804 by the seals813, 815 when the air gun 800 is in the armed position shown in FIG. 8A.

The piston 808 defines an inner port 810 that allows fluid communicationbetween the chambers 804, 806. The piston 808 includes a flange 812 inthe chamber 804 and a flange 816 in the chamber 806. A difference in theeffective area of the flanges 812, 816 may create a pressuredifferential across the piston 808 that secures the piston 808 in thearmed position shown in FIG. 8A. In some implementations, the piston 808may be pressure balanced when the piston 808 is in the armed position.In FIG. 8A, the chambers 804, 806 store compressed air, and the piston808 acts as a partition that prevents fluid communication between thechambers 804, 806 and the ports 818. In FIG. 8B, the piston 808 has beendisplaced and the ports 818 allow fluid communication from the chamber806 out of the pressure release assembly 802.

The control housing 801 defines a sealed chamber that contains theelectronic circuitry 820 and the solenoid valve 822. In someimplementations, the electronic circuitry 820 may be contained in one ormore sealed chambers separate from a sealed chamber that contains thesolenoid valve 822. In the example shown, the electronic circuitry 820and the solenoid valve 822 are secured in the control housing 801 byshock-absorbing material 819 in the control housing 801. The electroniccircuitry 820 may include a digital electronic controller, a memory, acommunication interface, a power supply, and/or different or additionalelectronic components. FIGS. 7, 10A, 10B, and 11 show example componentsand modules of electronic circuitry that may be housed in the controlhousing 801. The electronic circuitry 820 may receive power and/orcommunications from an external communication link through thecommunication link connector 824.

The solenoid valve 822 includes a housing 823 that contains a solenoid834 and a plunger 830. The solenoid valve 822 defines a solenoid valvechamber 832 within the housing 823. The solenoid valve 822 defines ports828, 826 that provide fluid communication between the solenoid valvechamber 832 and the ports 809, 807 of the pressure release assembly. Inthe armed position shown in FIG. 8A, the plunger 830 may seal to asealing surface within the solenoid valve chamber 832 to prevent fluidcommunication from the solenoid valve chamber 832 into the firing port807 of the pressure release assembly 802. In the firing position shownin FIG. 8B, the plunger 830 is moved from the sealing surface to allowfluid communication from the solenoid valve chamber 832 into the firingport 807 of the pressure release assembly 802. The solenoid 834 ismechanically coupled to the plunger 830 to move the plunger 830 inresponse to an electrical signal applied to the solenoid 834. Thesolenoid 834 is electrically coupled to the electronic circuitry 820,and the electronic circuitry 820 controls the electronic signal appliedto the solenoid 834. In some example solenoid valves, the solenoidincludes a conductive coil about a magnetic core, and the magnetic coreis mechanically coupled to the plunger. In such examples, the electricalsignal received by the solenoid generates a current in the conductivecoil, the current creates a magnetic field, and the magnetic fieldexerts a force on the magnetic core, which moves the plunger to open thesolenoid valve.

In one aspect of operation, the air gun 800 is configured as shown inFIG. 8A, and the air gun 800 is pressurized by an external source. Theair gun 800 receives pressurized air from the external source throughthe connector 836. The pressurized air flows into the chamber 804through the port 803. The pressurized air flows from the chamber 804into the other pressure chamber 806 through the port 810. Thepressurized air flows from the chamber 804 into the solenoid valvechamber 832 through the port 826. When the chambers 804, 806 havepressurized to a steady pressure, the pressure release assembly 802 isarmed, or ready to fire. In some implementations, the chambers 804, 806are pressurized to a latch pressure of 2000 psi, 3000 psi, or anotherpressure.

In one aspect of operation, the air gun 800 is initially configured asshown in FIG. 8A, and the pressure release assembly 802 is actuated. Forexample, the electronic circuitry 820 may fire the air gun in responseto or based on commands or instructions received from a command center.To fire the air gun 800, a power supply of the electronic circuitry 820is coupled to the solenoid valve 822. The power supply applies a voltagesignal to the solenoid 834 of the solenoid valve 822. The voltage signalapplied to the solenoid 834 moves the plunger 830 to open the port 828,as shown in FIG. 8B. For example, the voltage signal applied to thesolenoid 834 may energize a coil of the solenoid 834, thereby creating amagnetic field that acts on a magnetic core of the solenoid 834, whichin turn causes the magnetic core to move the plunger 830 away from theport 828. Movement of the plunger 830 opens the solenoid valve 822 andpermits fluid communication between the solenoid valve chamber 832 andthe firing port 807 of the pressure release assembly 802. The highpressure air communicated from the solenoid valve chamber 832 into thepressure release assembly 802 actuates the pressure release assembly802.

In one aspect of operation, the air gun 800 is configured as shown inFIG. 8B, and the pressure release assembly 802 generates an acousticsignal. In the example shown, the pneumatic signal from the solenoidvalve chamber 832 traverses the firing port 807 and creates a pressureimbalance on the piston 808. The pressure imbalance on the piston 808urges the piston into the pressure chamber 804, as shown in FIG. 8B.Movement of the piston 808 opens the ports 818, allowing the pressurizedair from the chamber 806 to exit the pressure release assembly 802through the ports 818. The release of pressurized air through the ports818 generates an acoustic signal in the water, represented in FIG. 8B bythe wave fronts 840.

FIGS. 9A and 9B are flow charts showing an example processes 900, 950for operating a marine air gun. In some implementations, the example airguns 322 a, 322 b, 323, 400, 500, 600, 800 shown in FIGS. 3A-6B, 8A, and8B and other marine air guns may operate in accordance with one or moreoperations of the processes 900, 950. One or more of the operations inthe processes 900, 950 may be performed by the electronic componentsand/or modules shown in FIGS. 7, 10A, 10B, and 11, and/or by othercomponents or modules. Each process 900, 950 may include different,additional, or fewer operations. The operations of each process 900, 950may be performed in the order shown or in a different order. In someimplementations, one or more of the operations of each processes 900,950 may be iterated and/or performed simultaneously with otheroperations. In some implementations, one or more of the operationsand/or subsets of the operations may be performed as part of a separateprocess or sub-process. Some of the processes and logic flows describedin this specification, including the processes 900, 950 and others, canbe carried out by one or more digital electronic controllers, which mayinclude digital logic circuitry, microcontrollers, and/or programmableprocessors, executing instructions to operate on input data and generateoutput data.

The process 900 may be implemented by digital electronic circuitryhoused at the marine air gun to control operation of a marine air gunbased on digital communications received from a command center (e.g.,the command center 106 of FIG. 1). At 902, an input signal is received.The input signal may be a voltage modulated electrical signal receivedby the air gun from a communication link external to the air gun. Theinput signal may include a command sent to the air gun from the commandcenter. At 904, electrical power from the input signal is stored by theair gun. For example the electrical power may be stored in capacitorsand/or other electrical devices housed in the air gun. At 906, digitalcommunications are decoded from the input signal. For example, acommunication interface at the air gun may convert voltage modulationsin the input signal to digital data. The digital communications and/ordigital data based on the communications may be stored in a memoryhoused in the air gun. The digital communications may instruct the airgun to perform an operation. For example, the digital communications mayinstruct the air gun to fire, to prepare to receive a fire command, tocollect data from a transducer, to perform a quality control test, totransmit a status message, to power up, to power down, and/or to performanother operation. At 908, the air gun uses the power from the inputsignal to perform the operation based on the received digitalcommunication. For example, the air gun may use the stored power to firethe air gun, the collect, digitize, store, and/or transmit data, and/orto perform other operations based on digital communications receivedfrom a command center. The air gun may alternatively or additionally usepower received by the air gun before or after receiving the inputsignal.

The process 950 may be implemented by digital electronic circuitryhoused at a marine air gun to collect digital data relating to operationof the marine air gun. At 952, data is collected by one or more sensors.The sensors may include sensors housed on the marine air gun and/orsensors housed apart from the marine air gun. The sensors may include apressure sensor, a water depth sensor, a near-field hydrophone, azero-field hydrophone, and/or others. The data collected by the sensorsmay be analog data. The data may be collected over a period of time, forexample, 10 milliseconds, 100 milliseconds, 1 second, or another periodof time. At 954, the data is digitized. The data may be digitized by adigitizer in the sensor, in an electronic controller, a separate A/Dconverter, and/or by another module. The digitizer may be housed at theair gun. For example, the digitizer may be housed in a sealed chamberdefined in a housing of the air gun. The data may be digitized at adigitization frequency. For example, the data may be digitized at 1 kHz,10 kHz, 100 kHz, and/or another frequency. At 956, the digitized data isstored. The digitized data may be stored in a memory of an electroniccontroller, a separate memory, in a logic device, in a machine-readablemedium, and/or in another type of component. The digitized data may bestored in a component housed at the air gun. For example, the memory maybe housed in a sealed chamber defined in a housing of the air gun. At958, the digitized data is transmitted from the air gun. The air gun caninclude a communication interface that transmits the digital data over acommunication link. The digitized data may be transmitted by a componenthoused at the air gun. For example, the communication interface may behoused in a sealed chamber defined in a housing of the air gun. Thedigital data may be transmitted by modulating current on thecommunication link.

FIGS. 10A and 10B are diagrams collectively showing an examplecommunication system for a marine seismic system. The communicationsystem includes an example air gun communication subsystem 1000 a housedat a marine air gun (e.g., any of the marine air guns shown anddescribed herein, including the air gun 1204 of FIG. 12, and/or others).In some instances, all or part of the air gun communication subsystem1000 a may be housed apart from the air gun, for example, on a hangerplate for an air gun cluster. The communication system includes anexample command center communication subsystem 1000 b housed at acommand center (e.g., the command center 106 of FIG. 1, the commandcenter 1202 of FIG. 12, and/or a different command center). In someinstances, all or part of the command center communication subsystem1000 b may be housed apart from the command center and/or apart from thevessel. In some implementations, either of the communication subsystems1000 a, 1000 b may interface with additional and/or differentcommunication subsystems. The communication subsystems 1000 a, 1000 bare described here as sharing bidirectional communications. In someimplementations, either of the communication subsystems 1000 a, 1000 bmay be implemented in a transmitter-only or receiver-only configuration.As such, the communication subsystems 1000 a, 1000 b can be modified forunidirectional communications. The communication subsystems 1000 a, 1000b each send and receive digital communications. In some implementations,one or both of the communication subsystems 1000 a, 1000 b sends and/orreceives analog communications in addition to or instead of digitalcommunications.

The air gun communication subsystem 1000 a housed at a marine air gunincludes a power and communications module 702, a low voltage supplymodule 706, a communication interface module 704, and a digitalelectronic controller module 710. The air gun communication subsystem1000 a may include fewer, additional and/or different components. Themodules 702, 704, 706, 710 may be configured and/or function as shownand described with respect to FIG. 7. As shown in the example air guncommunication subsystem 1000 a in FIG. 10A, the power and communicationmodule 702 includes a rectifier bridge 1004, the communication interfacemodule 704 includes a current modulator 1006 and a comparator 1012, andthe digital electronic controller includes a digital data transmitter1014 and a digital data receiver 1016. The modules 702, 704, 710 of theair gun communication subsystem 1000 a may include additional ordifferent components housed at the air gun and/or elsewhere.

The example power and communications module 702 receives input from twoconducting lines 1002 a, 1002 b. The conducting lines 1002 a, 1002 b maybe conductors of a twisted pair, a coaxial cable, and/or another type ofcommunication link. The conducting lines 1002 a, 1002 b may be includedin a communication link external the air gun and/or a communication linkconnector. In some implementations, the conducting lines 1002 a, 1002 beach carry a high or a low voltage. For example, when the conductingline 1002 a carries a high voltage (e.g., 20 Volts, 30 Volts, 40 Volts,or another voltage level), the other conducting line 1002 b carries alow voltage (e.g., 0 Volts, or another ground reference voltage); andwhen the conducting line 1002 a carries the low voltage, the otherconducting line 1002 b carries the high voltage.

In some instances, the conducting lines 1002 a, 1002 b may remain in aconstant state for a period of time, where the high voltage remains onone of the conducting lines and the low voltage remains on the otherconducting line. For example, when the air gun communication subsystem1000 a transmits data to the command center communication subsystem 1000b, the conducting line 1002 a may remain at the high voltage and theconducting line 1002 b may remain at the low voltage, or vice versa. Insome instances, the high voltage and low voltage may switch back andforth between the conducting lines 1002 a, 1002 b over time, forexample, at 10 kHz, 100 kHz, or another frequency. Digitalcommunications may be encoded in such voltage modulations on theconducting lines 1002 a, 1002 b.

The communication interface module 704 may detect incoming digitalcommunications based on voltage modulations on the conducting lines 1002a, 1002 b. In the example shown in FIG. 10A, the comparator 1012receives the input signal from both of the conducting lines 1002 a, 1002b and generates an output signal based on the inputs. The output signalmay be a binary voltage signal transmitted to the digital data receiver1016. The digital electronic controller module 710 may store thereceived message and/or perform operations (e.g., fire the air gunand/or another operation) in response to the received message.

The comparator 1012 can generate the binary voltage signal that itcommunicates to the digital data receiver 1016 by converting voltagedifferences on the conducting lines 1002 a, 1002 b to binary voltagesignals. For example, the comparator 1012 may convert a voltagedifference to a binary voltage signal by comparing the voltage on thefirst conducting line 1002 a and the voltage on the second conductingline 1002 b and generating the binary voltage signal based on thecomparison. As a specific example, the comparator 1012 may generate ahigh voltage signal when the voltage on the first conducting line 1002 ais higher than the voltage on the second conducting line 1002 b; and thecomparator 1012 may generate a low voltage signal when the voltage onthe second conducting line 1002 b is higher than the voltage on thefirst conducting line 1002 a. The low voltage supply module 706 and/or ahigh voltage supply module may receive electrical power from the powerand communication module 702 at the same time that the communicationinterface module 704 receives and/or transmits communications.

The communication interface module 704 may also send outgoing digitalcommunications to the command center communication subsystem 1000 bthrough the conducting lines 1002 a, 1002 b. The communication interfacemodule 704 may send digital communications by modulating current on oneor both of the conducting lines 1002 a, 1002 b. The command centercommunication subsystem 1000 b may detect the digital communicationsbased on the current modulations. The current modulator 1006 maymodulate current on the conducting lines 1002 a, 1002 b by toggling thestate of a transistor 1008 between a conducting and non-conductingstate. The transistor 1008 may be a field effect transistor, a bipolarjunction transistor, or a different type of electrical switch. Switchingthe transistor 1008 to a conducting state may increase the current onone or both of the conducting lines, and switching the transistor 1008to a non-conducting state may decrease the current on one or both of theconducting lines. In the example shown, the current modulator 1006includes a resistor 1010 in series between the transistor 1008 and aground reference voltage. The resistor may be a 5 ohm, 10 ohm, 15 ohm,20 ohm, or different level resistor. The state of the transistor 1008 iscontrolled by the digital data transmitter 1014. The digital datatransmitter 1014 may control the transistor 1008 by controlling a binaryvoltage signal applied to the transistor 1008. A different type ofcurrent modulator may be used.

The rectifier bridge 1004 converts a time-constant or time-varyingvoltage signal from the conducting lines 1002 a, 1002 b to atime-constant voltage signal. The rectifier bridge 1004 may include thefour-diode bridge shown in FIG. 10A and/or additional or differentcomponents. The rectified (time-constant) voltage signal from therectifier bridge 1004 is provided to the low voltage supply module 706.The low voltage supply module 706 may store electrical energy from thevoltage signal. The low voltage supply module 706 may condition, modify,and/or distribute the electrical energy to components of the air gun.

The command center communication subsystem 1000 b includes a powerinverter module 1050, a data transmitter module 1051, a voltage supplymodule 1052, a current change detector module 1053, a data receivermodule 1056, and a memory module 1058. The command center communicationsubsystem 1000 b may include additional and/or different components. Thevoltage supply module 1052 provides electrical voltage that can betransmitted to the air gun communication subsystem 1000 a housed at theair gun and/or used to power components of the command centercommunication subsystem 1000 b housed at the command center. In someimplementations, the voltage supply module 1052 provides a voltage of 30Volts, 40 Volts, 50 Volts, or another voltage.

The power inverter module 1050 may include an H-bridge device. In someimplementations, the H-bridge device includes a mover that modulates theelectrical output of the H-bridge at a high frequency. For example, themover may switch high and low voltage outputs of the H-bridge betweentwo output terminals at a high frequency. The power inverter module 1050outputs the electrical voltage from the voltage supply module 1052 tothe conducting line 1002 a or to the conducting line 1002 b. When thepower inverter module 1050 couples the voltage supply module 1052 to theconducting line 1002 a, the power inverter module 1050 couples theconducting line 1002 b to a ground reference voltage. When the powerinverter module 1050 couples the voltage supply module 1052 to theconducting line 1002 b, the power inverter module 1050 couples theconducting line 1002 a to a ground reference voltage. The power invertermodule 1050 may generate time-varying voltage differences across theconducting lines 1002 a, 1002 b by switching the high voltage outputbetween the conducting lines 1002 a, 1002 b over time. Digitalcommunications may be encoded in such voltage modulations. The digitalcommunications may be detected at the air gun, for example by thecomparator 1012 of FIG. 10A, based on the voltage modulations.

The data transmitter module 1051 may control the voltage modulationsapplied to the conducting lines 1002 a, 1002 b by sending binary voltagesignals to the power inverter module 1050. The power inverter module1050 may receive either a high or low binary signal from the datatransmitter module 1051, and the power inverter module 1050 may outputthe electrical voltage from the voltage supply module 1052 to one of thetwo conducting lines 1002 a, 1002 b based on the binary voltage signal.For example, when the power inverter module 1050 receives a high voltagesignal from the data transmitter module 1051, the power inverter module1050 may couple the conducting line 1002 a to the high voltage source(e.g., 40 Volts) and couple the conducting line 1002 b to a groundreference voltage (e.g., 0 Volts); and when the power inverter module1050 receives a low voltage signal from the data transmitter module1051, the power inverter module 1050 may couple the conducting line 1002b to the high voltage source and couple the conducting line 1002 a tothe ground reference voltage. The voltage difference across the twoconducting lines 1002 a, 1002 b may be modulated at a high frequency(e.g., 10 kHz, 100 kHz, or another frequency) to transmit digital data.

The current change detector module 1053 and the data receiver module1056 can detect incoming digital communications based on currentmodulations on the conducting lines 1002 a, 1002 b. The currentmodulations may be the current modulations generated by the currentmodulator 1006 in the air gun communication subsystem 1000 a. Thecurrent change detector module 1053 and/or the data receiver module 1056may include additional components that filter out small changes incurrent or noise. The current change detector module 1053 and the datareceiver module 1056 may detect incoming digital communication based oncurrent modulations by converting changes in current on the conductinglines 1002 a, 1002 b to binary voltage signals. The current changedetector 1053 may include transformers coupled to the conducting lines1002 a, 1002 b. The transformer coupled to each conducting line 1002 a,1002 b may convert current changes on the conducting line to voltagesignals on one or both of the output lines 1054 a, 1054 b. For example,the current change detector 1053 may convert an increase in current oneither conducting line to a voltage signal on the output line 1054 a,and the current change detector 1053 may convert a decrease in currenton either conducting line to a voltage signal on the output line 1054 b.

The data receiver module 1056 receives the signals from the output lines1054 a, 1054 b and generates a binary voltage signal based on thereceived signals. Data from the data receiver module 1056 may be storedin the memory module 1058. For example, each binary voltage signal fromthe data receiver module 1056 may be converted and/or stored as a bit ina binary memory of the memory module 1058. The data receiver module 1056may include a set-reset device and/or another type of flip-flop device.The output line 1054 a may be coupled to the set terminal of theset-reset device, and the output line 1054 b may be coupled to the resetterminal of the set-reset device, or vice versa. The output lines 1054a, 1054 b may both output a reference voltage signal when the current onthe conducting lines 1002 a, 1002 b is in a steady state. The outputline 1054 a may output a high voltage signal when the current on eitherof the conducting lines 1002 a, 1002 b increases. The high voltagesignal on the output line 1054 a may be communicated to the set terminalof the set-reset device, which may toggle the binary voltage signalgenerated by the set-reset device. Toggling the binary voltage signalmay change the signal from logical 1 to logical 0 or may change thesignal from logical 0 to logical 1. The output line 1054 b may output ahigh voltage signal when the current on either of the conducting lines1002 a, 1002 b decreases. The high voltage signal on the output line1054 b may be communicated to the reset terminal of the set-resetdevice, which may toggle the binary voltage signal generated by theset-reset device.

FIG. 11 is a diagram showing an example high voltage supply module 708of a marine air gun. The high voltage supply module 708 may receiveinput voltage signals from the conducting lines 1002 a, 1002 b of FIG.10A. In some implementations, the conducting lines 1002 a, 1002 b carrya voltage difference of 30 Volts, 40 Volts, or another voltage level.The input voltage signals may include time-varying and/or time-constantvoltage signals. A time-varying input voltage signal from the conductinglines 1002 a, 1002 b may be converted (e.g., by a rectifier bridge, oranother device) to a time-constant signal within the high voltage supplymodule 708 or prior to entering the high voltage supply module 708.

The high voltage supply module 708 may include two output leads 1106 a,1106 b. The output leads 1106 a, 1106 b may be communicably coupled toone or more of the electronic modules in FIG. 7 and/or additional ordifferent systems, subsystems, devices, or modules. The output leads1106 a, 1106 b may provide a voltage signal to an actuator (e.g., asolenoid valve, or another type of actuator) directly and/or indirectlythrough an actuator interface module. A digital electronic controllermay control the voltage signal from the high voltage supply module 708to the actuator by controlling the actuator interface module. Applyingthe voltage to the actuator may cause the actuator to actuate a pressurerelease assembly of the marine air gun. In some implementations, theoutput leads 1106 a, 1106 b carry a voltage difference of 60 Volts, 80Volts, or another voltage level.

In the example shown, the high voltage supply module 708 includes twodiodes 1102 a, 1102 b and two capacitors 1104 a, 1104 b. The highvoltage supply module 708 may include additional or differentcomponents. The capacitors 1104 a, 1104 b are connected with each otherin series. The conducting line 1002 b connects between the capacitors1104 a, 1104 b. The conducting line 1002 a splits to connect on eitherside of both capacitors 1104 a, 1104 b. The diodes 1102 a, 1102 b areconfigured to apply the voltage difference between the conducting lines1002 a, 1002 b across both capacitors 1104 a, 1104 b. The output leads1106 a, 1106 b tap the voltage across both capacitors 1104 a, 1104 b.Thus, the voltage difference between output leads 1106 a, 1106 b is thecombined voltage across both capacitors 1104 a, 1104 b. In someimplementations, the voltage difference between output leads 1106 a,1106 b is twice the voltage difference across the conducting lines 1002a, 1002 b. For example, if the conducting lines 1002 a, 1002 b have avoltage difference of 40 Volts, the output leads 1106 a, 1106 b can havea voltage difference of 80 Volts. The capacitors 1104 a, 1104 b may beidentical to each other or different. One or both of the capacitors mayinclude a electrolytic capacitor. One or both of the capacitors mayinclude hardened material, for example an aluminum casing, having robustmechanical properties. In some examples, the capacitors have acapacitance of 3300 microfarads, an equivalent series resistance of 44.0milliohm, a voltage rating of 80 Volts, and a tolerance of ±20%. Anexample of a capacitor that may be used is the MLP flatpack, aluminumcapacitor (e.g., part number MLP332M080EB0A) available fromCornell-Dubilier Electronics. Different types of capacitors may be used.

FIG. 12 is a signaling a flow chart showing an example process 1200 foroperating a marine seismic source system. For example, the process 1200may be used to operate some aspects of the system 100 of FIG. 1. Theprocess 1200 may include different, additional, or fewer operations. Theoperations of the process 1200 may be performed in the order shown or ina different order. In some implementations, one or more of theoperations of the processes 1200 may be iterated and/or performedsimultaneously with other operations. In some implementations, one ormore of the operations and/or subsets of the operations may be performedas part of a separate process or sub-process.

In FIG. 12, operations are represented as being performed by a commandcenter 1202 and/or an air gun 1204. In some implementations, anothertype of system or subsystem may perform one or more of the operationsshown. The air gun 1204 may be an air gun of an air gun array, submersedin water, and towed behind a vessel to perform a marine seismic survey.The command center 1202 may include devices and/or structures located onthe vessel and/or in different locations. The command center 1202 may bethe command center 106 of FIG. 1, and the air gun 1204 may be includedin one of the air gun clusters 120. In some implementations, the exampleair guns 322 a, 322 b, 323, 400, 500, 600, 800 shown in FIGS. 3A-6B, 8A,and 8B and other marine air guns may perform the operations of the airgun 1204. The process 1200 and/or some aspects of the process 1200 maybe repeated each time the air gun array of the seismic source systemgenerates a seismic signal. For example, the process 1200 may berepeated periodically (e.g., every second, 2 seconds, every 10 seconds,every minute, etc.) over several minutes or hours.

The communications in the process 1200 may be performed by thecommunications subsystems 1000 a, 1000 b of FIGS. 10A, 10B. The commandcenter communication subsystem 1000 b may perform one or more operationsof the command center 1202, and the air gun communication subsystem 1000a may perform one or more operations of the air gun 1204. Some or all ofthe operations in the process 1200 may be performed by digital and/oranalog electronic circuitry. Some or all of the communications in theprocess 1200 may be point-to-point digital communications between thecommand center 1202 and the air gun 1204. The communications in theprocess 1200 may be transmitted by one or more communication linksbetween the command center 1202 and the air gun 1204. The communicationlinks may include twisted pairs, fiber optics, coaxial cables, wirelesslinks, and/or others.

At 1210, the command center 1202 receives a nav closure signal. The navclosure signal may be sent to the command center 1202 from a navigationcenter on a vessel (e.g., the navigation center 104 of the vessel 102 inFIG. 1). The nav closure signal instructs the command center 1202 tofire the air gun array. In response to the nav closure signal, thecommand center 1202 sends an arm message 1212 to the air gun 1204. Insome implementations, the arm message 1212 is sent by the command center1202 fifty milliseconds after receiving the nav closure signal. An armmessage may be sent to each air gun in an air gun array. In someimplementations, the arm message 1212 is a 16-byte digital message. Thearm message 1212 may include or may be preceded by a header thatidentifies to which air gun(s) the arm message 1212 is addressed. In theexample shown, the arm message 1212 is addressed to the air gun 1204.The arm message 1212 may be received by and/or addressed to additionalair guns. In some implementations, the arm message 1212 may bedisregarded by one or more of the additional air guns. In someimplementations, one more of the additional air guns may react and/orrespond to the arm message 1212.

The arm message 1212 instructs the air gun 1204 to prepare to receive afire command. In response to the arm message 1212, the air gun 1204 mayinterrupt operation of a digital electronic controller of the air gun1204. Interrupting the digital electronic controller may allow thedigital electronic controller to receive and react to a fire commandpromptly. After sending the arm message 1212, the command center 1202sends a fire command 1216 to the air gun 1204. In some implementations,the fire command 1216 is sent by the command center 1202 twenty-fivemilliseconds after sending the arm message 1212. A fire command may besent to each air gun in an air gun array. In some implementations, thefire command 1216 is an electrical pulse applied to a communication linkbetween the command center 1202 and the air gun 1204. The fire command1216 may include or may be preceded by a header that identifies to whichair gun(s) the fire command 1216 is addressed.

After receiving the fire command 1216, the air gun 1204 waits a delaytime 1218. The delay time may vary for each air gun. For example, due tovariations among air guns, each air gun in an array may take a differentamount of time to fire. In some example air gun arrays, the firing timeamong air guns may vary by five to twenty milliseconds. Thus, each airgun has a firing delay time that can be adjusted individually for eachgun so that the air guns in the array all fire simultaneously. Thefiring delay time may be a variable stored in a memory of the air gun.After waiting the delay time, the air gun 1204 fires at 1220. When theair gun 1204 fires, a pressure release assembly of the air gun 1204releases an acoustic signal. To fire the air gun 1204, the digitalelectronic controller on the air gun 1204 may toggle a switch to couplethe air gun actuator to a power supply. The actuator may move inresponse to an electrical signal from the power supply, and movement ofthe actuator may actuate the pressure release assembly to generate theacoustic signal by releasing compressed air.

Before, during, and/or after the air gun 1204 fires, the air gun 1204collects data at 1222. For example, the air gun 1204 may collect datausing one or more sensors housed on or near the air gun 1204. Thesensors may include a pressure transducer, a depth transducer, azero-field hydrophone, a near-field hydrophone, and/or other types ofsensors. Data may be collected over several milliseconds, seconds orminutes. The air gun 1204 may digitize, store, and/or otherwise processthe collected data. After collecting data, the air gun sends a collecteddata message 1224 to the control center 1202. The collected data message1224 may include several digital messages transmitted over severalseconds or minutes. In some implementations, the collected data message1224 includes several kilobytes or megabytes of digital data. Thecollected data message 1224 may include or be preceded by an identifierthat identifies the air gun 1204 as the source of the message 1224. Thecommand center 1202 may receive a collected data message from each airgun in the array.

After receiving the collected data message 1224, the command center 1202analyzes data associated with the seismic source system at 1226. Thedata analysis may be performed by a computing system that runs dataprocessing software. The data analyzed by the command center 1202 mayinclude some or all of the data from the collected data message 1224and/or data from collected data messages received from other air guns inthe array. The data analyzed by the command center 1202 may includeadditional and/or different data. The data analysis may, among otherthings, identify the firing time of the air guns in the array. Forexample, the data analysis performed by the command center 1202 mayidentify the time at which the air gun 1204 fired. The data analysis mayidentify one or more air guns that did not fire at the target time,i.e., one or more air guns that did not fire simultaneously with theother air guns in the array. As part of the data analysis, the commandcenter 1202 may determine an updated delay time for the one or more airguns that did not fire at the target time, or the command center 1202may determine a delay time for all of the air guns. After the dataanalysis, the control center 1210 sends an update delay time message1228 to the air gun 1204. The update delay time message 1228 instructsthe air gun to store an updated delay time in its memory. The updateddelay time message 1228 can be a digital message, e.g., 16 bytes, 32bytes, or a different size. The next time the air gun 1204 receives afire command, the air gun 1204 waits for the updated delay time.Additional and/or different messages may be exchanged between thecommand center 1202 and the air gun 1204 before the next nav closuresignal and/or at different times during the process 1200.

Some aspects of the systems and techniques described in thisspecification can be implemented in a communication system that includesnetworked devices operating in a master-slave, client-server,peer-to-peer, and/or another type of relationship. In some instances,the components of the system can be interconnected by various forms ofdata communication. For example, the components may operate in thecontext of a digital communication network and/or a digitalpoint-to-point communication scheme. In some instances, analogcommunication schemes may be used. A communication network may includeany form of digital data communication, such as a local area network(“LAN”), Ethernet, another standard type of network, and/or an ad-hocnetwork. The components may communicate according to any suitablecommunication protocol, which may include synchronous and/orasynchronous digital communication protocols.

A number of implementations have been described. Nevertheless, it willbe understood that various modifications may be made. Accordingly, otherimplementations are within the scope of the following claims.

1. A marine air gun comprising: a pressure release assembly thatreleases compressed air into water to generate an acoustic signal; anactuator that moves to actuate the pressure release assembly in responseto an electrical signal applied to the actuator, the actuator carried bythe pressure release assembly; and a digital electronic controller thatcontrols the electrical signal applied to the actuator, the digitalelectronic controller carried by the pressure release assembly.
 2. Themarine air gun of claim 1, further comprising one or more sensorscarried by the pressure release assembly, the one or more sensorscomprising at least one of a depth transducer, a pressure transducer, ora zero-field hydrophone, the digital electronic controller comprising: adigitizer that receives analog data from the one or more sensors andconverts the analog data to digital data; and a memory that stores thedigital data.
 3. The marine air gun of claim 2, further comprising acommunication interface carried by the pressure release assembly, thecommunication interface configured to: transmit the digitized data fromthe digital electronic controller to a central control system externalthe marine air gun; and receive digital communications from the centralcontrol system, the digital communications comprising commands thatoperate the digital electronic controller.
 4. The marine air gun ofclaim 1, further comprising a high voltage supply carried by thepressure release assembly and electrically coupled to the actuator by aswitch, the digital electronic controller communicably coupled to theswitch to control the electrical signal applied to the actuator by thehigh voltage supply.
 5. The marine air gun of claim 4, the high voltagesupply comprising two capacitors each receiving an input voltage, thecapacitors connected in series to provide an output voltage twice theinput voltage.
 6. The marine air gun of claim 5, wherein at least one ofthe two capacitors is an electrolytic capacitor.
 7. The marine air gunof claim 1, further comprising a circuit board carried by the pressurerelease assembly, the circuit board comprising the digital electroniccontroller, a low voltage supply, a high voltage supply, and acommunication interface.
 8. The marine air gun of claim 1, the actuatorand the digital electronic controller residing in an actuator housingcarried by a separate housing of the pressure release assembly.
 9. Themarine air gun of claim 1, at least one of the actuator or the digitalelectronic controller residing in a chamber defined by a housing of thepressure release assembly.
 10. The marine air gun of claim 1, thepressure release assembly defining one or more ports and comprising: apressure chamber that stores the compressed air; and a partition thatprevents fluid communication between the chamber and the one or moreports, actuation of the pressure release assembly moves the partition topermit communication of the compressed air into the water from thechamber through the one or more ports.
 11. The marine air gun of claim10, the actuator comprising a solenoid valve, a component of thesolenoid valve moves to release a pneumatic signal in response to theelectrical signal applied to the actuator, the pneumatic signal movesthe partition to permit communication of the compressed air into thewater from the chamber through the one or more ports.
 12. A marineseismic system comprising: a sensor that detects conditions in or abouta marine air gun submersed in water; the marine air gun comprising: apressure release assembly that generates an acoustic signal; a digitizerthat converts analog data from the sensor to digital data, the digitizercarried by the pressure release assembly and communicably coupled to thesensor; and a memory that stores the digital data, the memory carried bythe pressure release assembly and communicably coupled to the digitizer.13. The marine seismic system of claim 12, the sensor comprising azero-field hydrophone carried by the pressure release assembly, thezero-field hydrophone detecting acoustic data in the water about themarine air gun.
 14. The marine seismic system of claim 12, the sensorcomprising a near-field hydrophone spaced apart from the marine air gun,the near-field hydrophone detecting acoustic data in the water about themarine air gun.
 15. The marine seismic system of claim 12, the sensorcomprising a depth transducer carried by the pressure release assembly,the depth transducer detecting a depth of the marine air gun below asurface of the water.
 16. The marine seismic system of claim 12, thesensor comprising a pressure transducer carried by the pressure releaseassembly, the pressure transducer detecting an internal pressure of achamber in the pressure release assembly.
 17. The marine seismic systemof claim 12, the sensor residing in a sensor housing carried by ahousing of the pressure release assembly, a digital electroniccontroller that includes the digitizer and the memory residing in acontrol housing carried by the housing of the pressure release assembly,the marine air gun further comprising a communication link between thesensor housing and the control housing.
 18. The marine seismic system ofclaim 12, further comprising a digital electronic controller thatincludes the digitizer and the memory, the sensor and the digitalelectronic controller residing in a control housing carried by a housingof the pressure release assembly, the sensor communicably coupled to thedigital electronic controller by a soldered connection in the controlhousing.
 19. The marine seismic system of claim 12, the marine air gunfurther comprising: a digital electronic controller that includes thedigitizer and the memory; and an actuator that moves to actuate thepressure release assembly in response to an electrical signal applied tothe actuator, the digital electronic controller controlling theelectrical signal applied to the actuator, the digital electroniccontroller and the actuator residing in a control housing carried by thepressure release assembly.
 20. A marine seismic system comprising: anarray of marine air guns, each marine air gun including: a pressurerelease assembly that generates an acoustic signal in water; an actuatorthat moves to actuate the pressure release assembly in response to anelectrical signal applied to the actuator; and a digital electroniccontroller that controls the electrical signal applied to the actuator,the digital electronic controller and the actuator carried by thepressure release assembly; and a central control subsystem communicablycoupled to each digital electronic controller to send power andcommunications to the marine air gun.
 21. The system of claim 20,further comprising a plurality of communication links that communicablycouple the central control subsystem to the array of marine air guns totransmit the power and communications.
 22. The system of claim 21, eachmarine air gun further including a communication interface thatcommunicably couples one of the communication links to the digitalelectronic controller.
 23. The system of claim 21, further comprising amultiplexer communicably coupled to the central control subsystem andthe plurality of communication links, the multiplexer configured to:receive multiplexed signals from the central control subsystem; generatea plurality of demultiplex signals from the multiplexed signals; andsend the plurality of demultiplexed signals to the marine air gunsthrough the communication links.
 24. The system of claim 21, the arraycomprising a plurality of air gun clusters, each of the air gun clusterscomprising one or two of the marine air guns, each communication linkproviding communication and power from the central control subsystem toa single cluster.
 25. The system of claim 20, each marine air gunfurther including a communication interface configured to transmitdigital data from the digital electronic controller of the marine airgun to the central control subsystem, the communication interfacecarried by the pressure release assembly.
 26. The system of claim 20,the central control subsystem residing on a marine vessel that tows thearray.
 27. A marine seismic system comprising: a plurality of air gunclusters, each air gun cluster including one or more marine air gunsthat generate acoustic signals in water based on digital communicationsfrom a central control subsystem, the central control subsystemcommunicably coupled to the plurality of air gun clusters by a pluralityof communication links, each of the communication links communicablycoupled to one of the air gun clusters to transmit the digitalcommunications from the central control subsystem to the air guncluster.
 28. The marine seismic system of claim 27, the communicationlink for each air gun cluster comprising a single twisted pair.
 29. Themarine seismic system of claim 28, each marine air gun clusterconfigured for bidirectional communication with the central controlsubsystem over the single twisted pair.
 30. The marine seismic system ofclaim 27, the communication link for each air gun cluster comprising afiber optic link.
 31. The marine seismic system of claim 27, each marineair gun comprising a digital electronic controller, the digitalcommunications comprising commands transmitted from the central controlsubsystem to the digital electronic controller.
 32. The marine seismicsystem of claim 27, each air gun comprising a sensor, the digitalcommunications comprising data collected by the sensor and transmittedfrom the marine air gun to the central control subsystem.
 33. A methodof communicating digital data in a marine seismic system, the methodcomprising: sending an outgoing digital communication to a marine airgun by modulating voltage on a communication link that communicablycouples the marine air gun to a central control subsystem; detecting anincoming digital communication from the marine air gun based on currentmodulations on the communication link; and storing the incoming digitalcommunication in a memory of the central control subsystem.
 34. Themethod of claim 33, wherein the incoming digital communication comprisesdigital data collected by sensors at the marine air gun and the outgoingdigital communication comprising digital command signals that controloperation of the marine air gun.
 35. The method of claim 33, wherein thecommunication link comprises a first conductive wire and a secondconductive wire, and modulating voltage on the communication linkcomprises switching between: a first voltage state in which the firstconductive wire is electrically coupled to a high voltage source and thesecond conductive wire is electrically coupled to a ground referencevoltage; and a second voltage state in which the second conductive wireis electrically coupled to the high voltage source and the firstconductive wire is electrically coupled to the ground reference voltage.36. The method of claim 35, wherein the high voltage source comprises a40 Volt direct current voltage source, and the ground reference voltagecomprises 0 Volts.
 37. The method of claim 33, wherein detecting anincoming digital communication from the air gun based on currentmodulations on the communication link comprises converting changes incurrent on the communication link to binary voltage signals.
 38. Themethod of claim 37, wherein a change in current is converted to a binaryvoltage signals by: outputting a first voltage signal based on detectingan increase in the current on the communication link; and outputting asecond voltage signal based on detecting a decrease in the current onthe communication link.
 39. A method of communicating digital data in amarine seismic system, the method comprising: sending an outgoingdigital communication from a marine air gun by modulating current on acommunication link that communicably couples the marine air gun to acentral control subsystem; detecting an incoming digital communicationfrom the central control subsystem based on voltage modulations on thecommunication link; and storing the incoming digital communication in amemory of the marine air gun.
 40. The method of claim 39, wherein theoutgoing digital communication comprises digital data collected bysensors at the marine air gun and the incoming digital communicationcomprises digital command signals that control operation of the marineair gun.
 41. The method of claim 39, wherein modulating current on thecommunication link comprises toggling an electrical coupling between thecommunication link and a ground reference voltage.
 42. The method ofclaim 41, wherein the electrical coupling comprises a switch and aresistor connected in series between the communication link and theground reference voltage, and toggling the electrical coupling compriseschanging the switch between a conductive state and a non-conductivestate.
 43. The method of claim 39, wherein detecting an incoming digitalcommunication from the central control subsystem based on voltagemodulations on the communication link comprises converting voltagedifferences on the communication link to binary voltage signals.
 44. Themethod of claim 43, wherein a voltage difference is converted to abinary voltage signal by: comparing a first voltage on a first conductorof the communication link and a second voltage on a second conductor ofthe communication link; outputting a first voltage state when the firstvoltage is higher than the second voltage; and outputting a secondvoltage state when the second voltage is higher than the first voltage.45. The method of claim 39, further comprising: receiving electricalpower from the communication link; and using the electrical power tooperate electronic circuitry of the marine air gun.
 46. The method ofclaim 45, wherein receiving the electrical power comprises receiving theelectrical power concurrently with detecting the incoming digitalcommunication.
 47. A marine seismic system comprising: a communicationlink that transmits digital data between a central control subsystem anda marine air gun; the central control subsystem including a voltagemodulator coupled to the communication link to transmitvoltage-modulated signals to the marine air gun; and the marine air gunincluding a current modulator coupled to the communication link totransmit current-modulated signals to the central control subsystem. 48.The marine seismic system of claim 47, wherein the voltage-modulatedsignals and the current-modulated signals each include at least one ofasynchronous digital communications or synchronous digitalcommunications.
 49. The marine seismic system of claim 47, thecommunication link comprising a twisted pair.
 50. The marine seismicsystem of claim 47, further comprising a plurality of additional airguns and a plurality of additional communication links, each additionalair gun including a current modulator coupled to one of the additionalcommunication links to transmit current-modulated signals to the centralcontrol subsystem.
 51. The marine seismic system of claim 50, thecentral control subsystem including a plurality of additional voltagemodulators each coupled to one of the additional communication links totransmit voltage-modulated signals to one of the air guns.
 52. Themarine seismic system of claim 47, the marine air gun comprising: acomparator that converts the voltage-modulated signals to binary data;and a memory that stores the binary data.
 53. The marine seismic systemof claim 47, the central control subsystem comprising: a set-resetdevice that converts the current-modulated signals to binary data; and amemory that stores the binary data.
 54. The marine seismic system ofclaim 47, the voltage modulator comprising an H-bridge.
 55. The marineseismic system of claim 47, the current modulator comprising atransistor.